Question

(15+x).(6+x)=136

Answer 1

\(\left(x+15\right)\left(x+6\right)=136\)

\(\Leftrightarrow x^2+21x-46=0\)

\(\Leftrightarrow\left(x+23\right)\left(x-2\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-23\\x=2\end{matrix}\right.\)

Answer 2

\(\left(15+x\right)\left(6+x\right)=136\)

\(\Leftrightarrow x^2+21x-46=0\)

\(\Leftrightarrow\left(x-2\right)\left(x+23\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x+23=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=-23\end{matrix}\right.\)

Answer 3

(15 + x)(6 + x) = 136

<=> 90 + 15x + 6x + x² = 136

<=> 90 + 21x + x² = 136

<=> x² + 21x - 46 = 0

<=> x² + 2x - 23x - 46 = 0

<=> x(x + 2) - 23(x + 2) = 0

<=> (x - 23)(x + 2) = 0

<=> \(\left[{}\begin{matrix}x-23=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=23\\x=-2\end{matrix}\right.\)