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91Ó°ÊÓ

use the Binomial Theorem to find the indicated coefficient or term

The coefficient of x2in the expansion of (2x -3)9

Short Answer

Expert verified

The coefficient of x2 is -144

Step by step solution

01

Step 1. Given information

(2x-3)9 is given..

we have to find coefficient of the term of x2

02

. Expansion of  (2x-3)9 using The Binomial Theorem 

The binomial theorem states that

Letxandaberealnumbers.Foranypositiveintegern,wehave(x+a)n=n0xn+n1axn-1+n2a2xn-2+.......+njajxn-j+.....+nnan

using this theorem we can expand the given expression, here a=1 and n=9


localid="1647339977970" (2x-3)9=90(2x)9+91(-1)(2x)9-1+92(-1)2(2x)9-2+............+97(-1)7(2x)9-7+98(-1)8(2x)9-8+99(-1)9=90(2x)9-91(2x)8+92(2x)7+........-97(2x)2+98(2x)1-99

03

Step 3. Description of finding the coefficient of x2

The coefficient of x2 from the expanded of the given expression is

97(2)2(-1)7,whichisequalto9!2!7!×22×(-1)7=-9×8×7!2×1×7!×4=-144

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