Question

x^2-2x-35
____________ /divided by (x^2-4x-21)
x^2+12x+35

Answer 1

(x^2-2x-35)/(x^2+12+35) /(x^2-4x-21)
is equal to
(x+5)(x-7) / ((x+5)(x+7)) / ((x-7)(x+3))

cancel out the factor

1/((x+7)(x+3))

or is equal to 1 over x^2 + 10x + 21