1.

If (x + 1) is a factor of x4 + 9x3 + 7x2 + 9ax + 5a2, then :(a) a = 137 (b) 5a2 – 9a – 1 = 0(c) 5a2 + 9a + 17 = 0 (d) a = \(\sqrt{131}\)

Answer»

(b) 5a2 – 9a – 1 = 0

Let f (x) = x4 + 9x3 + 7x2 + 9ax + 5a2

If (x + 1) is a factor of f (x), then 

f(–1) = 0 ⇒ (–1)4 + 9 (–1)3 + 7 (–1)2 + 9a (–1) + 5a2 = 0 

⇒ 1 – 9 + 7 – 9a + 5a2 = 0 ⇒ 5a2 – 9a – 1 = 0.



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