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Answer 1 · 2017-11-03T04:03:08

$(8+9d)(8-9d)$

Now this expression is a difference of squares.

Statistics Lecture

We know this because $64$ is a squared number $(8^2)$ , while $81$ is equal to $9^2$ , and $d^2$ is equal to $(d)^2$

If we apply this to our expression...

$64-81d^2$

$=(8+9d)(8-9d)$

Hope this helps :)

Answer 2 · 2017-11-03T04:06:00

$64-81d^2=color(blue)((8+9d)(8-9d)$

Factor:

$64-81d^2$

The two terms in this expression are square numbers.

$64=color(red)(8^2$

$81d^2=color(green)((9d)^2$

Factor the expression using the difference of squares:

$a^2-b^2=(a+b)(a-b)$

$color(red)(8^2)-color(green)((9d)^2)$ $=color(blue)((8+9d)(8-9d)$