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Find the locus of the point of intersection of tangents to the ellipse x^2/a^2 +y^2/b^2 = 1 at the points the sum of whose ordinates is constant(let it be c)
eq of ellipse = x2/a2 + y2/b2 = 1 ............1 eq of tangent of this ellipse is y = mx +(a2m2+b2)1/2 .............2 (m is slope of tangent) now we have to find point of intersection of this tangent & ellipse ,for that put eq 2 in 1 x2/a2 + [mx+(a2m2+b2)1/2]2/b2 = 1 x2(1/a2+m2/b2) + 2mx(a2m2+b2)1/2/b2 + (a2m2+b2)/b2 - 1 = 0 now it is given that the sum of ordinate is constant c , that means sum of roots of above equation is equal to c ... x1+x2 = C (sum of roots = -b/a) -[2m(a2m2+b2)1/2 /b2 ] / [1/a2+m2/b2] = C squaring both sides & after simplifing we get m2 = C2b2/a2(4a2-c2) ...................3 now , tangent will pass through point of intersection of tangents so let point of intersection is (A,B) then this point will satisfy the eq of tangent so locus is B = mA + (a2m2+b2)1/2 (from eq 2) now substitute value of m in above eq & replace (A,B) by (X,Y) this will give the required locus..... approve my ans if u like it
eq of ellipse = x2/a2 + y2/b2 = 1 ............1
eq of tangent of this ellipse is y = mx +(a2m2+b2)1/2 .............2 (m is slope of tangent)
now we have to find point of intersection of this tangent & ellipse ,for that put eq 2 in 1
x2/a2 + [mx+(a2m2+b2)1/2]2/b2 = 1
x2(1/a2+m2/b2) + 2mx(a2m2+b2)1/2/b2 + (a2m2+b2)/b2 - 1 = 0
now it is given that the sum of ordinate is constant c , that means sum of roots of above equation is equal to c ...
x1+x2 = C (sum of roots = -b/a)
-[2m(a2m2+b2)1/2 /b2 ] / [1/a2+m2/b2] = C
squaring both sides & after simplifing we get
m2 = C2b2/a2(4a2-c2) ...................3
now , tangent will pass through point of intersection of tangents so let point of intersection is (A,B) then
this point will satisfy the eq of tangent so
locus is B = mA + (a2m2+b2)1/2 (from eq 2)
now substitute value of m in above eq & replace (A,B) by (X,Y) this will give the required locus.....
approve my ans if u like it
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