Question

(x+1)(x+7)=72 , x=?

Answer 1

(x+1)(x+7)=72
x²+7x+x+7=72
x²+8x=72-7=65
x(x+8)=65
65=5·13
x+8=13
x=5

Answer 2

[tex](x+1)(x+7)=72\\ x^2+x+7x+7=72\\ x^2+8x-65=0\\ \Delta=64+4\cdot 65=324\Rightarrow \sqrt{\Delta}=18\\ x_1=\frac{-8+18}{2}=5\\ x_2=\frac{-8-18}{2}=-13\\ S:x\in \{5,-13\}[/tex]