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Question
Evaluate: (2x – 5y)(2x + 3y) for x = 2 and y = 3.
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Solution
(2x – 5y) (2x + 3y)
= 2x × 2x − 5y × 2x + 2x × 3y − 5y × 3y
= 4x2 − 10xy + 6xy − 15y2
Hence, x = 2 and y = 3
4x2 − 10xy + 6xy − 15y2
= 4(2)2 − 10(2)(3) + 6(2)(3) − 15(3)2
= 16 − 60 + 36 − 135
= 52 − 195
= −143
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