How do you multiply $(7x-y)(8x+9y)$ ?

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Answer 1 · 2015-12-04T08:53:08

$=color(blue)(56x^2 + 55xy -9y^2$

$(color(blue)(7x)-color(purple)(y))(8x+9y)$

$= color(blue)((7x) * (8x) + (7x) * (9y) )+ color(purple)( (-y) * (8x) + (-y) * (9y)$

$=56x^2 + 63xy -8xy -9y^2$

$=color(blue)(56x^2 + 55xy -9y^2$

How do you multiply (7x-y)(8x+9y)(7x-y)(8x+9y)?