x^2 + y^2 = 25

Question

3x + y = 15
Find the two points of intersection.

I don't just want the answer, if you could tell me how to find it, it would save my life. The sqaure root is making it really hard for me to understand.

Answer 1

from the second,y=15-3x

then square it...

225-90x+9x^2 check that, and put it in for y^2 in the first equation, rearrange it in quadratic form, and solve for x using the quadratic formula.