solve the equations algebraically

Question

x^2 + y^2 = 25
3y - 4x = 0

Answer 1

I would use substitution, from the 2nd ....
y = 4x/3
sub into the first ....
x^2 + (4x/3)^2 = 25
x^2 + 16x^2/9 = 25
9x^2 + 16x^2 = 225
25x^2 = 225
x^2 = 9
x = ± 3

if x=3, y = 4
if x = -3 , y = -4