Question

Simplify: (x + 9) (x + 8).
A. x2 + 17x + 72
B. x2 + 72x + 17
C. x2 + 17
D. x2 + 72

Answer 1

\[\begin{align}
\text{F.O.I.L. = First Outside Inside Last}\\
\hline \\
&(ax+b)(cx+d)\\ \ \\
\text{First:}&(\color{blue}{ax}+b)(\color{blue}{cx}+d)\to \color{blue}{ax}\cdot\color{blue}{cx}=\color{blue}{acx^2}\\
\text{Outside:}&(\color{green}{ax}+b)(cx+\color{green}{d})\to \color{green}{ax}\cdot\color{green}{d}=\color{green}{adx}\\
\text{Inside:}&(ax+\color{red}{b})(\color{red}{cx}+d)\to \color{red}{b}\cdot\color{red}{cx}=\color{red}{bcx}\\
\text{Last:}&(ax+\color{orange}{b})(cx+\color{orange}{d})\to \color{orange}{b}\cdot\color{orange}{d}=\color{orange}{bd}\\
\hline \\
(ax+b)(cx+d)&=\color{blue}{acx^2}+\color{green}{adx}+\color{red}{bcx}+\color{orange}{bd}
\end{align}\]

Answer 2

x2+17x+72. A. Try to do it yourself. here try this one: (x+6)(x+10)

Answer 3

Use formula (x+a)(x+b) = x^2+ax +bx + ab
And solve.