Question 658497
x^2-4x=21
X^2-4X-21=0
(X-7)(X+3)=0
X-7=0
X=7 ANS.
X+3=0
X=-3 ANS.
PROOFS:
-7^2-4*-7=21
49+28=21
21=21
-3^2-4*-3=21
9+12=21
21=21