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Question
Using algebraic identity, find the coefficients of x2, x and constant term without actual expansion
(2x + 3)(2x – 5)(2x – 6)
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Solution
(2x + 3)(2x – 5)(2x – 6)
∴ Co-efficient of x2 = 4 (a + b + c)
= 4(3 + (– 5) + (– 6))
= 4 × (– 8) = – 32
Co-efficient of x = 2 (ab + bc + ca)
= 2[3 × (– 5) + (– 5)(– 6) + (– 6)(3)]
= 2[–15 + 30 – 18] = 2 × (– 3) = – 6
Constant term = abc
= 3 × (– 5) × (– 6)
= 90
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