Question

please give me answer

Answer 1

using formula a^2 -b^2 =(a+b)(a-b)

so the sum can be written as :
( 3x+7y +3x -7y)(3x +7y -3x +7y)
:- (6x) (14y) =84xy



hope you helped. plz mark me brainliest answer.

Answer 2

I'll gonna use two formula's
(i) $(a+b)^2 = a^2 + 2ab + b^2$
(ii) $(a-b)^2 = a^2 - 2ab + b^2$

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$(3x+7y)^2 - (3x-7y)^2$
$= \{ (3x)^2 + 2\cdot3x\cdot7y + (7y)^2 \} - \{ (3x)^2 - 2\cdot3x\cdot7y + (7y)^2 \}$
$= \{ 9x^2 + 42xy + 49y^2 \} - \{ 9x^2 - 42xy + 49y^2 \}$
$= \cancel{9x^2} + 42xy + \cancel{49y^2} - \cancel{9x^2} + 42xy - \cancel{49y^2}$
$= 84xy$