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@Chew-Seong Cheong , we really liked your comment, and have converted it into a solution. If you subscribe to this solution, you will receive notifications about future comments.
3 3 2 4 3 3 2 5 4 3 2 ⋯ 1 0 9 3 2 3 2 2 1 × 3 1 3 2 3 1 × 4 1 3 2 4 1 × 5 1 . . . 3 2 9 1 × 1 0 1 3 2 2 . 3 1 + 3 . 4 1 + 4 . 5 1 + . . . + 9 . 1 0 1 3 2 5 2 4
As Jake Lai has pointed out. It's better to mention that you used telescoping sum because it's the key to simplify the calculation.
Might help to show that it's a telescoping sum.
The fractional exponents are: 3 1 ∗ 2 1 , 4 1 ∗ 3 1 , . . . n 1 ∗ n − 1 1 , . . . 1 0 1 ∗ 9 1 .
This makes the series: n = 3 ∏ 1 0 ( 3 2 n ( n − 1 ) 1 )
Because a m ∗ a n = a m n , this in turn is: n = 3 ∏ 1 0 ( 3 2 n ( n − 1 ) 1 ) = 3 2 ∑ n = 3 1 0 ( n ( n − 1 ) 1 )
The series ∑ n = 2 m ( n ( n − 1 ) 1 ) = m m − 1 , but since we're starting at n = 3 , we'll need to subtract the value where n = 2 . (A quick substitution shows this to be 2 1 .)
So: n = 3 ∑ m ( n ( n − 1 ) 1 ) = n = 2 ∑ m ( n ( n − 1 ) 1 ) − 2 1 = 1 0 1 0 − 1 − 2 1 = 1 0 9 − 2 1 = 1 0 4 = 5 2
Thus: n = 3 ∏ 1 0 ( 3 2 n ( n − 1 ) 1 ) = 3 2 ∑ n = 3 1 0 ( n ( n − 1 ) 1 ) = 3 2 5 2 = 2 5 5 2 = 2 2 = 4
Sum of the exponents of 32 are 2 . 3 1 + 3 . 4 1 + 4 . 5 1 + . . . . . . + 9 . 1 0 1 which adds up to 2 1 − 1 0 1 = 5 2 as exponent of 32. Answer = 4
Similar method as Rajen Kapur
n = 1 ∏ 8 [ ( 3 2 ) n + 1 1 ] n + 2 1 = n = 1 ∏ 8 [ ( 2 5 ) n + 1 1 ] n + 2 1 = n = 1 ∏ 8 [ 2 n + 1 5 ] n + 2 1 = n = 1 ∏ 8 2 ( n + 1 ) ( n + 2 ) 5 = 2 ∑ n = 1 8 ( n + 1 ) ( n + 2 ) 5 = 2 5 ∑ n = 1 8 ( n + 1 1 − n + 2 1 ) = 2 5 ( 2 1 − 1 0 1 ) = 2 2 = 4
It goes like that: A=sqrt of 3(sqrt(32)) sqrt of 4(sqrt of 3(32)) ...* sqrt of 10(sqrt of 9(32)) =(32^(1/2 * 1/3)) (32^(1/3 * 1/4)) ...*(32^(1/9 * 1/10)) =32^( 1/2 * 1/3 + 1/3 * 1/4 +...+ 1/9 * 1/10 )=32^X
X=1/2 * 1/3 + 1/3 * 1/4 + ... + 1/9 * 1/10 =1/2 - 1/3 + 1/3 - 1/4 + ... + 1/9 - 1/10 =1/2 - 1/10 = 2/5
A=32^(2/5)=4 Nice one.
How did you get: 1/2 * 1/3 + 1/3 * 1/4 + ... + 1/9 * 1/10 equals this: 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/9 - 1/10
32^(1/2.3+1/3.4+1/4.5+.................+1/9.10) 1/2.3=1/2-1/3 1/3.4=1/3-1/4 so (1/2-1/3)+(1/3-1/4)+(1/4-1/5).................(1/9-1/10) =1/2-1/10 =====>2/5 32^(2/5) =======>((32)^1/5)^2===========>2^2=4
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n = 1 ∏ 8 [ ( 3 2 ) n + 1 1 ] n + 2 1 = n = 1 ∏ 8 [ ( 2 5 ) n + 1 1 ] n + 2 1 = n = 1 ∏ 8 [ 2 n + 1 5 ] n + 2 1 = n = 1 ∏ 8 2 ( n + 1 ) ( n + 2 ) 5 = 2 ∑ n = 1 8 ( n + 1 ) ( n + 2 ) 5 = 2 5 ∑ n = 1 8 ( n + 1 1 − n + 2 1 ) = 2 5 ( 2 1 − 1 0 1 ) = 2 2 = 4