-1x^2 + 10x - 21 = 0
-1(x^2-10x+21)=0
-1(x )(x ) ( -7)( -3)=0
-1(x-7) (x-3) = 0
Solve:
-1(x-7)=0
-1(x) (-1)(-7)=0
-1x+7=0
-1x+7-7=0-7
-1x=-7
-1x/-1=-7/-1
x=7
Solve:
-1(x-3) = 0
-1(x) (-1)(-3) = 0
-1x+3=0
-1x+3-3=0-3
-1x=-3
-1x/-1=-3/-1
x=3