JEE MainMathematicsSequences and SeriesNumerical+4 / −1
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 .
Numerical answer
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Correct answer: 40
- Set up the G.P. terms
Since are in G.P. and , let for some and common ratio .
We are given:
Substitute the G.P. terms.
- Use the second equation first
From we get Since , As are G.P. terms, taking , divide by : Factorizing, So,
- Use the first equation
From we get
Now test the two possible values of .
Case 1:
Then So the equation becomes which gives But this contradicts .
So this case is rejected.
Case 2:
Then Hence
Thus,
- Find the required value
We need Substitute:
- Final answer
The derived answer matches the stored correct answer.
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