Find sum of coefficient in expansion of
$(4 x + 7 y)^{2} - (4 x - 7 y)^{2}$

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Solution

$f o r m u l a u s e d$
$a^{2} - b^{2} = (a + b) (a - b)$
$G i v e n$
${(4 x + 7 y)}^{2} - {(4 x - 7 y)}^{2}$
$= (4 x + 7 y + 4 x - 7 y) (4 x + 7 y - 4 x + 7 y)$
$= (8 x) (14 y)$
$= 112 x y$

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