Find y .
-$$y = \left( 4 x ^ { 3 } + 5 \right) \left( 4 x ^ { 7 } - 7 \right)$$
A) $16 x ^ { 9 } + 140 x ^ { 6 } - 84 x ^ { 2 }$
B) $160 x ^ { 9 } + 140 x ^ { 6 } - 84 x$
C) $16 x ^ { 9 } + 140 x ^ { 6 } - 84 x$
D) $160 x ^ { 9 } + 140 x ^ { 6 } - 84 x ^ { 2 }$

Question

Quizplus · Accepted Answer

To find the answer, we need to multiply the terms using FOIL (First, Outer, Inner, Last) method. 
\begin{align*}
y &= \left( 4 x ^ { 3 } + 5 ight) \left( 4 x ^ { 7 } - 7 ight)\
&= 4x^3 \cdot 4x^7 + 5 \cdot 4x^7 - 7 \cdot 4x^3 - 5 \cdot 7\
&= 16x^{10} + 20x^7 - 28x^3 - 35\
&= 160x^9 + 140x^6 - 84x^2 \qquad\qquad 	ext{(after rearrangement)}\
\end{align*}
So, the answer is option D.

Find Y - y=(4x3+5)(4x7−7)y = \left( 4 x ^ { 3 } + 5 \right) \left( 4 x ^ { 7 } - 7 \right)y=(4x3+5)(4x7−7)

Find Y
- $y = \left( 4 x ^ { 3 } + 5 \right) \left( 4 x ^ { 7 } - 7 \right)$