Question

solve the system by method of substitution:
-x+y=-9
x^2+y^2=81

Answer 1

solve the first equation for y

-x + y = -9

y = x+9

plug x+9 in for y in the next equation solve the quadratic formula for x.

Answer 2

k thanks!!!

Answer 3

you're welcome

Answer 4

i now have x^2+18x+81=81.will the 81's cancel each other out? @tomo

Answer 5

x^2+y^2=81

x^2 + (x+9)^2 = 81

x^2 + x^2 + 18x + 81 = 81

subtract 81 from both sides

2x^2 + 18x = 0

2x^2 = -18x

x^2 = -9x

x^2 + 9x = 0

x*(x+9) = 0

// one solution
x = 0

// other solution
x+9 = 0

x = -9