Mathematics
If (x - 2) is a factor of 2x3 - x2 - px - 2,
(i) find the value of p
(ii) with the value of p, factorize the above expression completely.
Factorisation
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Answer
(i) Let f(x) = 2x3 - x2 - px - 2
Since, (x − 2) is the factor, f(2) = 0.
⇒ 2(2)3 - (2)2 - p(2) - 2 = 0
⇒ 16 - 4 - 2p - 2 = 0
⇒ 10 - 2p = 0
⇒ 2p = 10
⇒ p =
⇒ p = 5.
Hence, the value of p = 5.
(ii) f(x) = 2x3 - x2 - 5x - 2
Now, dividing f(x) by (x - 2), we get :
2x3 - x2 - 5x - 2 = (x - 2)(2x2 + 3x + 1)
= (x - 2)(2x2 + 2x + x + 1)
= (x - 2)[2x(x + 1) + 1(x + 1)]
= (x - 2)(2x + 1)(x + 1)
Hence, 2x3 - x2 - 5x - 2 = (x - 2)(2x + 1)(x + 1).
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