Question

expand the following with sutaible identites (a) (7x - 2y)wholeraiseto3 .

Answer 1

Hey !

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${(7x - 2y) }^{3} \\ \\ Using \: identity \\ \\ {(a-b)}^{3} = {a}^{3} - {b}^{3} - 3{a}^{2}b + 3a{b}^{2} \\ \\ {7x}^{3} - {2y}^{3} - 3{(7x)}^{2}(2y) + 3(7x){(2y)}^{2} \\ \\ {343x}^{3}- {8y}^{3} - 3({49x}^{2})(2y) + 3(7x){(8y)}^{2} \\ \\ {343x}^{3} - {8y}^{3} -294{x}^{2}y + 168{y}^{2}x$

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Answer 2

Heya!
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◾Expand => ( 7x - 2y )³

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➡Using the Identity => ( a - b )³ = a³ - b³ - 3a²b + 3ab²

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Here a = 7x , b = 2y

=> ( 7x )³ - ( 2y )² - 3 ( 7x )² ( 2y ) + 3 ( 7x ) ( 2y )²

=> 343x³ - 8y³ - 3 ( 49x² ) ( 2y ) + 3 ( 7x ) ( 4y² )

=> 343x³ - 8y³ - 294x²y + 168y²x

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