If 3x-7y= 8 and xy=-1, then this find the value of 9x²+49y²
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3x-7y =8
squaring both the side we get
(3x-7y)^2 = (8)^2
9x^2+49y^2 -42xy = 64
9x^2+49y^2 = 64 + 42 [xy=1]
= 106
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