Question 43748
x^2 + y^2 = 25
y^2 = 25 - x^2
so:
16x^2 + 25y^2 = 400
16x^2 + 25(25 - x^2) = 400
16x^2 + 625 - 25x^2 = 400
-9x^2 = -225
x^2 = 25
x = +-5
Plug:
x^2 + y^2 = 25 and x^2 + y^2 = 25
5^2 + y^2 = 25 and (-5)^2 + y^2 = 25
y^2 = 0 and y^2 = 0
y = 0 and y = 0
(5,0) and (-5,0)
{{{ graph( 600, 600, -10, 10, -10, 10, sqrt(-x^2 + 25), -sqrt(-x^2 + 25), sqrt((-16/25)x^2 + 16), -sqrt((-16/25)x^2 + 16) ) }}}