Posted by Anal-G on Friday, January 14, 2011 at 8:11am.
Find the equation of a locus of a point which moves so that the sum of its distance from (2,0)and (-2,0) is 8.
it is about equation of a locus..
- Analytic Geometry - Reiny, Friday, January 14, 2011 at 9:12am
Your description defines an ellipse.
does the question expect you to find that equation by using that definition?
if so, then let such a point on that locus be P(x,y)
√[(x-2)^2 + y^2] + √[(x+2)^2 + y^2] = 8
√[(x-2)^2 + y^2] = 8 - √[(x+2)^2 + y^2]
square both sides and expand
x^2 - 4x + 4 + y^2 = 64 - 16√[(x+2)^2 + y^2] + x^2 + 4x + 4 + y^2
16√[(x+2)^2 + y^2] = 64 + 8x
2√[(x+2)^2 + y^2] = 8 + x
squaring again and simplifying I get
3x^2 + 4y^2 = 48
divide each term by 48 to get it into standard form
x^2/16 + y^2/12 = 1
or, the easy way
from the description 2a = 8 , a = 4
(2,0) and (-2,0) must be the focal points so the midpoint or (0,0) must be the centre and c = 2
since the focal points lie on the x-axis
b^2 + c^2 = a^2
b^2 + 4 = 16
b^2 = 12
standard form with centre (0,0) is
x^2/a^2 + y^2/b^2 = 1
x^2/16 +y^2/12 = 1
Answer This Question
More Related Questions
- Analytic Geometry - Please help me to solve this problem. Find the equation of ...
- Maths - Find the equation of the locus of the point P(x,y) which moves so that ...
- Locus- Calculus - Find the equation of the locus of the point representing z if...
- math - I need help with parametric equations, locus problems, tell me how to ...
- locus - if a moving point p is always equidistant from the point A(2,4) and the ...
- add maths - A point moves such that its distance from point A(1,0) is twice its ...
- maths --plse help me.. - without using set square or protacter construct 1. ...
- add maths - A point P moves so as to satisfy the ratio OP:PA=1:3,where O is the ...
- geometry - A moving point is always equidistant from (5,3) and the line 3x+y+5=0...
- Geo (locus) - I don't fully get this stuff but some of these I guessed on and ...