Answer:
x² + x - 72 = (x + 9)(x - 8)
Step-by-step explanation:
[tex]x^2+x-72\quad \implies\quad a=1\,,\quad b=1\,,\quad c=-72\\\\x=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}\\\\x=\dfrac{-1\pm\sqrt{1^2-4\cdot1\cdot(-72)}}{2\cdot1}=\dfrac{-1\pm\sqrt{1+288}}{2}=\dfrac{17\pm\sqrt{289}}{2}\\\\x_1=\dfrac{-1-17}{2}=-9\quad,\qquad x_2=\dfrac{-1+17}{2}=8\\\\\\x^2+x-72=(x-(-9))(x-8)=(x+9)(x-8)[/tex]
or:
x² + x - 72 =
= x² + 9x - 8x - 72 =
= x(x + 9) - 8(x + 9) =
= (x + 9)(x - 8)
