Question
Find the product.
$(x+7y)(7x-y)$
$(x+7y)(7x-y)$
✓
Answer
$(x+7 y)(7 x-y)$
$=(x) \times(7 x-y)+(7 y) \times(7 x-y) $
$ =(x \times 7 x)-(x \times y)+(7 y \times 7 x)-(7 y \times y) $
$ =7 x^2-x y+49 x y-7 y^2 $
$ =7 x^2+48 x y-7 y^2 \quad \text {[adding like terms]}$
$=(x) \times(7 x-y)+(7 y) \times(7 x-y) $
$ =(x \times 7 x)-(x \times y)+(7 y \times 7 x)-(7 y \times y) $
$ =7 x^2-x y+49 x y-7 y^2 $
$ =7 x^2+48 x y-7 y^2 \quad \text {[adding like terms]}$
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