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Find the constant term in the binomial expansion \((2x^{2} +...

Find the constant term in the binomial expansion (2x2+1x)9

A.

84

B.

168

C.

336

D.

672

Correct answer is D

Let the power of 2x2 be t and the power of 1xx1 = 9 - t.

(2x2)t(x1)9t=x0

Dealing with x alone, we have

(x2t)(x9+t)=x02t9+t=0

3t9=0

The binomial expansion is then,

^{9}C_{3} (2x^{2})^{3}(x^{-1})^{6} = \frac{9!}{(9-3)! 3!} \times 2^{3}

= 84 x 8

= 672