Question
Multiply:
$ {[-3 d+(-7 f)](5 d+f)} $

Answer

To multiply, we will use distributive law as follows:
$ {[-3 d+(-7 f)](5 d+f)} $
$ =(-3 d)(5 d+f)+(-7 f)(5 d+f) $
$=\left(-15 d^2-3 d f\right)+\left(-35 d f-7 f^2\right) $
$ =-15 d^2-3 d f-35 d f-7 f^2 $
$ =-15 d^2-38 d f-7 f^2 $
Thus, the answer is $-15 d^2-38 d f-7 f^2 $.

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