Question

3x -7y=8 and xy=-1 find value of 9x2 + 49y2​

Answer 1

3x - 7y = 8

xy = -1

So,

$(3x - 7y)^{2}=(8)^{2}$

$(3x)^{2}+(7y)^{2}-(2*3x *7y)=64$

$9x^{2}+49y^{2}-(42xy)=64$

$9x^{2}+49y^{2}-(42*-1)=64$

$9x^{2}+49y^{2}+42=64$

$9x^{2}+49y^{2}=64-42$

Therefore,

$9x^{2} +49y^{2} = 22$

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