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4. If 5x – 2y = 7 and xy = 2, find the value of (5x + 2y)?.
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Consider the given equation,
Given 5x - 2y = 7 and xy =2 We know, (a + b)2 = a2 + b2 + 2ab or (a + b)2 = a2 + b2 - 2ab + 4ab = (a - b)2 + 4 ab So,
(5x+2y)2 = ( 5x - 2y)2 + 4× 5x × 2y) = 49 + 40 xy
so, (5x+2y)2 = 49 + 40 x 2 = 129.
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