Question

1-x+x²-x³ to obtain x³


please tell the answer​

Answer 1

Answer:

The expression 1+x+x2+...∞

forms GP. so applying sum of GP to infinite

terms we have

1+x+x2+...=1−x1    [∵S∞=1−ra]

So,

(1+x+x2+...)3=(1−x)−3

Applying Binomial Theorem for

negative index we have

(1−x)−3=1+3C1x+4C2x2+5C3x3+...

⇒ coeff. of x3 is 5C3=10

Explanation:

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