Question

Factorise : x^2+x-72 Step by Step​

Answer 1

Answer:

              x² + x - 72 = (x + 9)(x - 8)

Step-by-step explanation:

$x^2+x-72\quad \implies\quad a=1\,,\quad b=1\,,\quad c=-72\\\\x=\dfrac{-b\pm\sqrt{b^2-4ac}}{2a}\\\\x=\dfrac{-1\pm\sqrt{1^2-4\cdot1\cdot(-72)}}{2\cdot1}=\dfrac{-1\pm\sqrt{1+288}}{2}=\dfrac{17\pm\sqrt{289}}{2}\\\\x_1=\dfrac{-1-17}{2}=-9\quad,\qquad x_2=\dfrac{-1+17}{2}=8\\\\\\x^2+x-72=(x-(-9))(x-8)=(x+9)(x-8)$

or:

     x² + x - 72 =

= x² + 9x - 8x - 72 =

= x(x + 9) - 8(x + 9) =

= (x + 9)(x - 8)

Answer 2

Answer:

(x + 9)(x - 8)

Step-by-step explanation:

f(x) = x^2 + x - 72

     = x^2 - 8x + 9x - 72

     = (x^2 - 8x) + (9x - 72)

     = x(x - 8) + 9(x - 8)

     = (x + 9)(x - 8)