Question

Show that
(3x+7)² - 84x=(3x-7)²​

Answer 1

(3x+7)² - 84x

= 9x²+42x+49-84x

= 9x²-42x+49

= (3x-7)² Proved.

Answer 2

$\large\underline{\underline\red{LHS = (3x + 7)² − 84x}}$

ㅤ

$\large{\underline\green{Using , (a + b)² = a² + 2ab + b²}}$

ㅤ

$\large\pink{= (9x² + 42x + 49) − 84x}$

$\large\orange{= 9x² − 42x + 49}$

ㅤ

$\large{\underline\purple{Using , (a − b)² = a² − 2ab + b²}}$

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$\large\blue{= (3x)² − 2 (3x) (7) + (7)²}$

$\large\underline{\underline\red{= (3x − 7)² = RHS}}$