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Question
Multiply and then evaluate:
(4x + y) and (x – 2y); when x = 2 and y = 1.
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Solution
(4x + y) × (x − 2y)
= 4x (x − 2y) + y (x − 2y)
= 4x2 − 8xy + xy − 2y2
= 4x2 − 7xy − 2y2
Verification:
When x = 2, y = 1
L.H.S. = (4x + y) (x − 2y)
= (4 × 2 + 1) (2 − 2 × 1)
= (8 + 1) (2 − 2)
= 9 × 0
= 0
R.H.S. = 4x2 − 7xy − 2y2
= 4 (2)2 − 7 × 2 × 1 − 2 (1)2
= 4 × 4 − 14 − 2
= 16 − 16
= 0
∴ L.H.S. = R.H.S.
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