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Most Important Selected Qs for JEE AdvancedMathematicsSequences and Series

If a= _ r=1 ^ 1 r^2 , b= _ r=1 ^ 1 (2 r-1)^2 , then 3 a b is equal to

Correct answer

1.33

Step-by-step solution

aligned & a = _ r =1 ^ 1 r ^2 , ~b = _ r =1 ^ 1 (2 r -1)^2 & a = 1 1^2 + 1 2^2 + 1 3^2 + 1 4^2 + and b= 1 1^2 + 1 3^2 + 1 5^2 + 1 7^2 + & b = ( 1 1^2 + 1 2^2 + 1 3^2 + 1 4^2 + )- ( 1 2^2 + 1 4^2 + 1 6^2 + ) & b= ( 1 1^2 + 1 2^2 + 1 3^2 + 1 4^2 + )- 1 2^2 (1+ 1 2^2 + 1 3^2 + ) & b=a- 1 4 a & b=a 3 4 & a b = 4 3 aligned

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