Question

How is this solved?
r2 + 2r = 80

Answer 1

8,-10

Explanation:

r²+2r=80

r²+2r-80=0

r²+(10-8)r-80=0

r²+10r-8r-80=0

r(r+10)-8(r+10)=0

(r-8)(r+10)=0

either, or,

r-8=0 r+10=0

r=8 r=-10