Mathematics
If x - 3 is a factor of x2 + kx + 15; the value of k is :
8
3
-5
-8
Factorisation
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Answer
By factor theorem,
If x - a is the factor of polynomial f(x), then remainder f(a) = 0.
Given,
x - 3 is a factor of x2 + kx + 15.
Then substituting x = 3 in polynomial we get, remainder = 0 :
⇒ 32 + 3k + 15 = 0
⇒ 9 + 3k + 15 = 0
⇒ 3k + 24 = 0
⇒ 3k = -24
⇒ k = = -8.
Hence, Option 4 is the correct option.
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