Question

(3x + 7y)² – (3x - 7y)²
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Answer 1

84xy

Step-by-step explanation:

$(3x + 7y) {}^{2} - (3x - 7y) {}^{2}$

let consider the following formula

$(a + b) {}^{2} - (a - b) {}^{2} \\ = {a }^{2} + {b}^{2} + 2ab - ( {a}^{2} + {b}^{2} - 2ab) \\ = {a }^{2} + {b}^{2} + 2ab - {a }^{2} - {b}^{2} + 2ab \\ = 4ab$

here a=3x and b=7y

Therefore 4ab=4×3x×7y=84xy

The needed ans is 84xy.

Answer 2

Answer:

Holla mate

your answer is 84xy

Step-by-step explanation:

(3x+7y)^2-(3x-7y) ^2

• (a+b)^2=a^2+b^2+2ab
• (a-b) ^2=a^2+b^2-2ab

Therefore by applying this formula we will get

=(3x) ^2+(7y) ^2+2(3x)(7y) -[(3x) ^2+(7y) ^2-2(3x)(7y) ]

=9x^2+49y^2+42xy-(9x^2+49y^2-42xy)

=9x^2+49y^2+42xy-9x^2-49y^2+42xy

=84xy (because 9x^2+49y^2 -9x^2-49y^2 will cancel each other)

Hope it helps you

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