Question

if 3x-7y =10 and xy=-1, the value of 9x²+49y².
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Answer 1

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Given, 3x−7y=10 and xy=−1.

Squaring on both sides

(3x−7y)² =10²

We know, (a−b)²

=a²−2ab+b²

Then,

⟹(3x)²+(7y)²−2(3x)(7y)=100

⟹9x²+49y²−42xy=100

⟹9x²+49y²=100−42 =58.

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Answer 2

Answer:

the given conditions are

3x-7y=10

xy=1

9x^2+49y^2

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

=(3x-7y) ^2+2.3x.7y

=(10) ^2+42 [put all the conditions]

=100+42

=142