Q56 / 90 · JEE Main 2022 (26 Jun Shift 2) · Mathematics

If a1(>0),a2,a3,a4,a5 are in a G.P. ,  a2+a4=2a3+1 and 3a2+a3=2a4, then a2+a4+2a5 is equal to _____.

Correct answer: 40

Solution

Given, a1>0,a2,a3,a4,a5→G.P.

3a2+a3=2a4

Using the formula an=arn-1 and assuming a1=a we get, 3ar+ar2=2ar3

⇒3+r=2r2

⇒2r2-r-3=0

⇒r=-1 & r=32

Also, a2+a4=2a3+1

⇒ar+ar3=2ar2+1

⇒ar+r3-2r2=1

⇒a32+278-184=1

⇒a=83

When r=-1,a=-14  (rejected, a1>0)

So, at r=23, a=83 

Now a2+a4+2a5

=83×32+83×278+2×83×8116

=4+9+27=40

Hence, the correct answer is 40.

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