Science > Mathematics > Coordinate Geometry > Locus > Equation of Locus
In this article, we shall study the concept of locus and to find the equation of the locus.
Locus: A set of points satisfying some geometrical condition or conditions is called as the locus
For example, a circle is a locus of all the points in the plane which are equidistant from the point in the plane.
Equation of Locus: The equation of locus is an equation which is satisfied by all the points satisfying given the geometrical condition in the problem
Steps Involved in Finding Equation of Locus:
- Assume the locus point P(x, y)
- Write given geometrical condition
- Use distance, section, centroid, and other formulae as per condition
- Substitute in geometrical condition. Simplify to get the equation of locus
Example – 01:
Find the locus of a point P such that its ordinate is 5.
Solution:
Let P(x. y) be the point on the locus
Given ordinate of P is 5 i.e. y = 5
Hence required equation of the locus of point P is y = 5.
Example – 02:
Find the locus of a point P such that its abscissa is 3.
Solution:
Let P(x. y) be the point on the locus
Given abscissa of P is 3 i.e. x = 3
Hence required equation of the locus of point P is y = 3
Example – 03:
Find the locus of a point P such that its ordinate is equal to the abscissa.
Solution:
Let P(x. y) be the point on the locus
Given ordinate of P is equal to the abscissa
Hence required equation of the locus of point P is y = x or x – y = 0
Example – 04:
Find the locus of a point P such that its ordinate exceeds 5 times its abscissa by 9
Solution:
Let P(x. y) be the point on the locus
Given ordinate of P exceeds 5 times its abscissa by 9
Hence required equation of the locus of point P is y = 5x + 9.
Example – 05:
Find the locus of a point P such that its abscissa exceeds 2 times its abscissa by 3
Solution:
Let P(x. y) be the point on the locus
Given abscissa of P exceeds 2 times its abscissa by 3
Hence required equation of the locus of point P is x = 2y + 3.
Example – 06:
Find the locus of a point P such that the sum of its coordinates is 15
Solution:
Let P(x. y) be the point on the locus
Given the sum of its coordinates is 15
Hence required equation of the locus of point P is x + y = 15
Example – 07:
Find the locus of a point P such that the sum of its coordinates is 10
Solution:
Let P(x. y) be the point on the locus
Given the sum of its coordinates is 10
Hence required inequality of the locus of point P is x + y = 10
Example – 08:
Find the locus of a point P such that the sum of its coordinates is less than 10
Solution:
Let P(x. y) be the point on the locus
Given the sum of its coordinates is less than 10
Hence required inequality of the locus of point P is x + y < 10
Example – 09:
Find the locus of a point P such that the sum of its coordinates is greater than 5
Solution:
Let P(x. y) be the point on the locus
Given the sum of its coordinates is greater than 5
Hence required inequality of the locus of point P is x + y > 5
Example – 10:
Find the locus of a point P such that the sum of squares of its coordinates is 25
Solution:
Let P(x. y) be the point on the locus
Given the sum of squares of its coordinates is 25
Hence required equation of the locus of point P is x² + y² = 25
Example – 11:
Find the locus of a point P such that the sum of square its coordinates is 9
Solution:
Let P(x. y) be the point on the locus
Given the sum of square of its coordinates is 9
Hence required inequality of the locus of point P is x² + y² = 9
Example – 12:
Find the locus of a point P such that twice the ordinate of P exceeds thrice its abscissa by 4.
Solution:
Let P(x. y) be the point on the locus
Given twice the ordinate of P exceeds thrice its abscissa by 4.
Hence required equation of the locus of point P is 2y = 3x + 4
Example – 13:
Find the locus of a point P such that the distance of P from x-axis equal to 10 times its distance from the y-axis.
Solution:
Let P(x. y) be the point on the locus
Distance from x-axis = y
Distance from y-axis = x
Given the distance of P from x-axis equal to 10 times its distance from y-axis
Hence required equation of the locus of point P is y = 10x
Example – 14:
Find the locus of a point P such that the distance of P from x-axis equal to its distance from the y-axis.
Solution:
Let P(x. y) be the point on the locus
Distance from x-axis = y
Distance from y-axis = x
Given the distance of P from x-axis equal to its distance from y-axis
Hence required equation of the locus of point P is y = x
Example – 15:
Find the locus of a point P such that the distance of P from origin equals 5 times its distance from the point (3, -2)
Solution:
Let P(x. y) be the point on the locus, Let O(0, 0) be the origin and A(3, -2) be the point
Given OP = 5 PA
∴ OP² = 25 PA²
∴ (x – 0)² + (y – 0)² = 25[(x – 3)² + (y + 2)²]
∴ x² + y² = 25[x² – 6x + 9 + y² + 4y + 4]
∴ x² + y² = 25x² – 150x + 225 + 25y² + 100y + 100
∴ 25x² – 150x + 225 + 25y² + 100y + 100 – x² – y² = 0
∴ 24x² + 24y² – 150x + 100y + 325 = 0
Hence required equation of the locus is 24x² + 24y² – 150x + 100y + 325 = 0
Example – 16:
Find the equation of locus of a point which is equidistant from the points (2, 3) and (-4, 5)
Solution:
Let P(x. y) be the point on the locus, Let A(2, 3) and B(-4, 5) be the given points
Given PA = PB
∴ PA² = PB²
∴ (x – 2)² + (y – 3)² = (x + 4)² + (y – 5)²
∴ x² – 4x + 4 + y² -6y + 9 = x² + 8x + 16 + y² – 10y + 25
∴ x² – 4x + 4 + y² -6y + 9 – x² – 8x – 16 – y² + 10y – 25 = 0
∴ – 12x + 4y -28 = 0
∴ 3x – y + 7 = 0
Hence required equation of the locus is 3x – y + 7 = 0
Example – 17:
Find the equation of locus of a point which is equidistant from the points (1, 2) and (3, 4)
Solution:
Let P(x. y) be the point on the locus, Let A(1, 2) and B(3, 4) be the given points
Given PA = PB
∴ PA² = PB²
∴ (x – 1)² + (y – 2)² = (x – 3)² + (y – 4)²
∴ x² – 2x + 1 + y² – 4y + 4 = x² – 6x + 9 + y² – 8y + 16
∴ x² – 2x + 1 + y² -4y + 4 – x² + 6x – 9 – y² + 8y – 16 = 0
∴ – 2x + 1 -4y + 4 + 6x – 9 + 8y – 16 = 0
∴ 4x + 4y – 20 = 0
∴ x + y – 5 = 0
Hence required equation of the locus is x + y – 5 = 0
Example – 18:
Find the equation of locus of a point which is equidistant from the points (2, 3) and (5, 7)
Solution:
Let P(x. y) be the point on the locus, Let A(2, 3) and B(5, 7) be the given points
Given PA = PB
∴ PA² = PB²
∴ (x – 2)² + (y – 3)² = (x – 5)² + (y – 7)²
∴ x² – 4x + 4 + y² – 6y + 9 = x² – 10x + 25 + y² – 14y + 49
∴ x² – 4x + 4 + y² – 6y + 9 – x² + 10x – 25 – y² + 14y – 49 = 0
∴ 6x + 8y – 61 = 0
Hence required equation of the locus is 6x + 8y – 61 = 0
Example – 19:
A(2, 3), B(-2, 5) are given points. Find the equation of locus of point P, such that PA = 2PB.
Solution:
Let P(x. y) be the point on the locus, Given A(2, 3) and B(-2, 5) be the given points
Given PA = 2 PB
∴ PA² = 4 PB²
∴ (x – 2)² + (y – 3)² = 4[(x + 2)² + (y – 5)²]
∴ x² – 4x + 4 + y² – 6y + 9 = 4[ x² + 4x + 4 + y² – 10y + 25]
∴ x² – 4x + 4 + y² – 6y + 9 = 4 x² + 16x + 16 + 4y² – 40y + 100
∴ 4 x² + 16x + 16 + 4y² – 40y + 100 – x² + 4x – 4 – y² + 6y – 9 = 0
∴ 3 x² + 3y² + 20x – 34y + 103 = 0
Hence required equation of the locus is 3 x² + 3y² + 20x – 34y + 103 = 0
Example – 20:
A(2, 3), B(-2, 1) are given points. Find the equation of locus of point P, such that AP² = 3 BP².
Solution:
Let P(x. y) be the point on the locus, Given A(2, 3) and B(-2, 1) be the given points
Given AP² = 3 BP²
∴ (x – 2)² + (y – 3)² = 3[(x + 2)² + (y – 1)²]
∴ x² – 4x + 4 + y² – 6y + 9 = 3[ x² + 4x + 4 + y² – 2y + 1]
∴ x² – 4x + 4 + y² – 6y + 9 = 3x² + 12x + 12 + 3y² – 6y + 3
∴ 3x² + 12x + 12 + 3y² – 6y + 3 – x² + 4x – 4 – y² + 6y – 9 = 0
∴ 2x² + 2y² + 16x + 2 = 0
∴ x² + y² + 8x + 1 = 0
Hence required equation of the locus is x² + y² + 8x + 1 = 0
Example – 21:
A(3, 1), B(4, -5) are given points. Find the equation of locus of point P, such that AP²+ BP² = 50.
Solution:
Let P(x. y) be the point on the locus, Given A(3, 1) and B(4, -5) be the given points
Given AP²+ BP² = 50.
∴ (x – 3)² + (y – 1)² + (x – 4)² + (y + 5)² = 50
∴ x² – 6x + 9 + y² – 2y + 1 + x² – 8x + 16 + y² + 10y + 25 = 50
∴ 2x² + 2y² – 14x + 8y + 51= 50
∴ 2x² + 2y² – 14x + 8y + 1 = 0
Hence required equation of the locus is 2x² + 2y² – 14x + 8y + 1 = 0
Example – 22:
A(-3, 2), B(1, -4) are given points. Find the equation of locus of point P, such that 3PA = 2 PB
Solution:
Let P(x. y) be the point on the locus, Given A(-3, 2) and B(1, -4) be the given points
Given 3 PA = 2 PB
∴ 9 PA²= 4 PB²
∴9[ (x + 3)² + (y – 2)²] = 4[(x – 1)² + (y + 4)²]
∴ 9( x² + 6x + 9 + y² – 4y + 4) = 4(x² – 2x + 1 + y² + 8y + 16)
∴ 9 x² + 54x + 81 + 9y² – 36y +36 = 4x² – 8x + 4 + 4y² + 32y + 64
∴ 9 x² + 54x + 81 + 9y² – 36y +36 – 4x² + 8x – 4 – 4y² – 32y – 64 = 0
∴ 5x² + 5y² + 62x – 68y +49 = 0
Hence required equation of the locus is 5x² + 5y² + 62x – 68y +49 = 0
Example – 23:
Find the equation perpendicular bisector of segment joining points (-5, 2) and (-1, 5)
Solution:
Let P(x. y) be the point on the locus, Let A(-5, 2) and B(-1, 5) be the given points
Perpendicular bisector of a line segment is locus of all the points
in the plane whci is equidistant from the endpoints of the segment
Hence PA = PB
∴ PA² = PB²
∴ (x + 5)² + (y – 2)² = (x + 1)² + (y – 5)²
∴ x² + 10x + 25 + y² -4y + 4 = x² + 2x + 1 + y² – 10y + 25
∴ x² + 10x + 25 + y² -4y + 4 – x² – 2x – 1 – y² + 10y – 25 = 0
∴ 8x + 6y + 3 = 0
Hence required equation of the locus (perpendicular bisector) is 3x – y + 7 = 0
Example – 24:
A(4, 5), B(-2, 7) are given points. Find the equation of locus of point P, such that 2PA = PB
Solution:
Let P(x. y) be the point on the locus, Given A(4, 5) and B(-2, 7) be the given points
Given 2PA = PB
∴ 4 PA²= PB²
∴4[ (x -4 )² + (y – 5)²] = (x + 2)² + (y – 7)²
∴ 4( x² – 8x + 16 + y² – 10y + 25) = x² + 4x + 4 + y² – 14y + 49
∴ 4x² – 32x +64 + 4y² – 40y + 100 = x² + 4x + 4 + y² – 14y + 49
∴ 4x² – 32x +64 + 4y² – 40y + 100 – x² – 4x – 4 – y² + 14y – 49 = 0
∴ 3x² + 3y² – 36x – 26 y +111 = 0
Hence required equation of the locus is 3x² + 3y² – 36x – 26 y + 111 = 0
Example – 25:
Find the equation of locus of points whose distance from the point (2, -3) is twice its distance from (1, 2).
Solution:
Let P(x. y) be the point on the locus, Given A(2, -3) and B(1, 2) be the given points
Given PA = 2 PB
∴ PA²= 4 PB²
∴ (x – 2 )² + (y + 3)² = 4[ (x – 1)² + (y – 2)²]
∴ x² – 4x + 4 + y² + 6y + 9 = 4[x² – 2x + 1 + y² – 4y + 4]
∴ x² – 4x + 4 + y² + 6y + 9 = 4x² – 8x + 4 + 4y² – 16y + 16
∴ 4x² – 8x + 4 + 4y² – 16y + 16 – x² + 4x – 4 – y² – 6y – 9 = 0
∴ 3x² + 3y² – 4x – 22 y + 7 = 0
Hence required equation of the locus is 3x² + 3y² – 4x – 22 y + 7 = 0
Example – 26:
Find the equation of locus of a point such that, the difference of square of its distances from the points (5, 0) and (2, 3) is 10.
Solution:
Let P(x. y) be the point on the locus, Given A(5, 0) and B(2, 3) be the given points
Given PA² – PB² = 10
∴ [(x – 5 )² + (y – 0)² ] – [(x – 2)² + (y – 3)²] = 10
∴ ( x² – 10x + 25 + y²) – (x² – 4x + 4 + y² – 6y + 9) = 10
∴ x² – 10x + 25 + y² – x² + 4x – 4 – y² + 6y – 9 – 10 = 0
∴ – 6x + 6y + 2 = 0
∴ 3x – 3y – 1 = 0
Hence required equation of the locus is 3x – 3y – 1 = 0
Example – 27:
Find the equation of locus of a point such that, the sum of the square of its distances from the points (2, -3) and (-1, -2) is 15.
Solution:
Let P(x. y) be the point on the locus, Given A(2, -3) and B(-1, -2) be the given points
Given PA² + PB² = 15
∴ [(x – 2 )² + (y + 3)² ] + [(x + 1)² + (y + 2)²] = 15
∴ x² – 4x + 4 + y² + 6y + 9 + x² + 2x + 1 + y² + 4y +4 – 15 = 0
∴ 2x² + 2y² – 2x +10y + 3 = 0
Hence required equation of the locus is 2x² + 2y² – 2x +10y + 3 = 0
Example – 28:
A(5, -6), B(-1, 2) and C(4, -3) are three given points. Find the equation of locus of points P such that PA² + PC² = AB².
Solution:
Let P(x. y) be the point on the locus, Given A(5, -6), B(-1, 2) and C(4, -3) be the given points
Given PA² + PC² = AB²
∴ [(x – 5 )² + (y + 6)² ] + [(x – 4)² + (y + 3)²] = (-1 – 5)² + (2 + 6)²
∴ x² – 10x + 25 + y² + 12y + 36 + x² – 8x + 16 + y² + 6y +9 = 36 + 64
∴ 2x² + 2 y² – 18x + 18 y – 14 = 0
∴ x² + y² – 9x + 9y – 7 = 0
Hence required equation of the locus is x² + y² – 9x + 9y – 7 = 0
Example – 29:
A(5, -6), B(-1, 2) and C(4, -3) are three given points. Find the equation of locus of points P such that PA² – PB² = 12.
Solution:
Let P(x. y) be the point on the locus, Given A(5, -6), B(-1, 2) and C(4, -3) be the given points
Given PA² – PB² = 12
∴ [(x – 5 )² + (y + 6)² ] – [(x + 1)² + (y – 2)²] =12
∴ (x² – 10x + 25 + y² + 12y + 36) – (x² + 2x + 1 + y² – 4y + 4) = 12
∴ x² – 10x + 25 + y² + 12y + 36 – x² – 2x – 1 – y² + 4y – 4 – 12 = 0
∴ – 12x + 16y + 44 = 0
∴ 3x – 4y – 11 = 0
Hence required equation of the locus is 3x – 4y – 11 = 0
Example – 30 :
Find the equation of locus of a point such that its distance from the origin is three times its distance from the x-axis.
Solution:
Let P(x. y) be the point on the locus, O(0. 0) be the origin
Distance of point from x-axis = y
Given: OP = 3y
∴ OP² = 9y²
∴ [(x – 0 )² + (y – 0)² ] = 9y²
∴ x ² + y ² = 9y²
∴ x ² – 8y ² = 0
Hence required equation of the locus is x ² – 8y ² = 0
9 replies on “Equation of Locus: Set – I”
was very helpful!!
Yes indeed……this is a great work…..Excelent work.
Very easy to understand
That’s a very good explanation
Excellent, easy to understand. Thanks for your explanation.
This is awesomely awesome!Well broken. Great job 👍👌
great job done I appreciate thanks
Number of examples are taken.
It’s excellent and very helpful for us.
I like it.
This is a very good page that I benefits alot from it and I will entreat colleagues to also use this page.