5x - 2y =7 and xy= 2, find the value of (5x+ 2y ) ^2
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Answer:
5x - 2y = 7
Squaring on both sides:
(5x - 2y)^2 = 7^2
25x^2 + 4y^2 - 20xy = 49
25x^2 + 4y^2 = 49 + 20(xy)
Put xy = 2:
25x^2 + 4y^2 = 49 + 40
25x^2 + 4y^2 = 89
(5x + 2y)^2 = 25x^2 + 4y^2 + 20xy
Put value of 25x^2 + 4y^2 And also, xy = 2:
89 + 20(2)
89 + 40
129
Thus, (5x + 2y)^2 = 129
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