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Question

If (1+x+x2)2n=a0+a1x+a2x2+........+a4nx4n, then

A
a0+a2+a4+......+a2n=14(9n1+2a2n)
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B
a0+a2+a4+......+a2n=14(9n+1+2a2n)
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C
a0+a2+a4+......+a2n=14(9n12a2n)
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D
a0+a2+a4+......+a2n=14(9n+12a2n)
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Solution

The correct option is A a0+a2+a4+......+a2n=14(9n+1+2a2n)
(1+x+x2)2n=a0+a1(x)+a2x2+...a4nx4n
For x=1, we get
9n=a0+a1+a2+...a4n ... (i)
For x=1 we get
1=a0a1+a2...a4n ... (ii)
Adding, (i) and (ii), we get
9n+1=2[a0+a2+a4+...a4n]

9n+12=a0+a2+a4+...a4n
And ar=a4nr
Now the middle term will be a2n
Hence
12[9n+1]=2[a0+a2+...a2n1]+a2n

12[9n+1]=2[a0+a2+...a2n]a2n

12[9n+1]=2[a0+a2+...a2n]2a2n2

12[9n+1+2a2n]=2[a0+a2+...a2n]

14[9n+1+2a2n]=a0+a2+...a2n

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