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If (7x - 10y) = 8 and xy = 5, then what is the value of $49x^2 +100y^2$? |
764 632 623 746 |
764 |
(7x - 10y) = 8 and xy = 5 We know that, (a - b)2 = a2 + b2 - 2ab = (7x - 10y)2 = 82 = 49x2 + 100y2 - 2 × 7x × 10y = 64 = 49x2 + 100y2 - 140xy = 64 = 49x2 + 100y2 = 64 + 140xy = 49x2 + 100y2 = 64 + 140 × 5 = 49x2 + 100y2 = 764 |
