Q36 of 39 Page 91

If 5x – 2y = 7 and xy = 2 find the value of (5x + 2y)2

(5x + 2y)2 = 5x2 + 2y2 + 2 × 5x × 2y


= 5x2 + 2y2 – 2 × 5x × 2y + 2 × 5x × 2y + 2 × 5x × 2y


= (5x – 2y)2 + 4 × x × y


= 72 + 4 × 2


= 49 + 8


= 57


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