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akshat very easy question it is
Nice solution
BTW, it would've been way cooler if the title would've been Put (Them all) in LOL (No offence to anyone)
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Can't understand! Please explain :-P
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Understanding things is an art that comes from within :P
same here C:
I had the right idea but got confused with the algebra.
Nice solution. Can you write out the formulas that you used for the sum of n , the sum of n 2 , and the sum of n 3 ? It would make your process much more clear.
If you know the formulae for the sums of n, n squared and n cubed, you can do it quite quickly.
Considering that the the sum of n(1+n+n^2) can be expanded to n+n^2+n^3, we can apply the following formulas:
Sum of n= (n (n+1))/2 Sum of n squares (n^3)/3 + (n^2)/2 + n/6 Sum of n cubes= ((n (n+1))/2)^2
We substitute: (10x11)/2 + 1000/3 + 100/2 + 10/6 + ((10x11)/2)^2
Which equals to 55 + 385 + 3025 = 3465
You rewrite the sum as: (k(k+1)/2)(1+(2k+1)/3 + k(k+1)/2), where k = 10 => 55(1+7+55) (= 55(60+3) = 165 + 3300)=3465 The steps in parentheses are for not doing any computer calculation.
= ∑ n = 1 1 0 n + ∑ n = 1 1 0 n 2 + ∑ n = 1 1 0 n 3 = 2 1 0 ⋅ 1 1 + 6 1 0 ⋅ 1 1 ⋅ ( 2 ⋅ 1 0 + 1 ) + ( 2 1 0 ⋅ 1 1 ) 2 = 5 5 + 3 8 5 + 5 5 2 = 4 4 0 + ( 5 ⋅ 6 ⋅ 1 0 0 + 2 5 ) = 4 4 0 + 3 0 2 5 = 3 4 6 5
10×11/2+{(10)×(10+1)×(10×2+1)}/6+(10^2)(10+1)^2/4 =55+385+3025 =3465
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n = 1 ∑ 1 0 n ( 1 + n + n 2 ) = n = 1 ∑ 1 0 n + n 2 + n 3 = 2 1 0 ⋅ 1 1 + 6 1 0 ⋅ 1 1 ⋅ 2 1 + ( 2 1 0 ⋅ 1 1 ) 2 = 5 5 + 3 8 5 + 5 5 2 = 3 4 6 5
Formulae used: n = 1 ∑ k n = 2 k ( k + 1 ) n = 1 ∑ k n 2 = 6 k ( k + 1 ) ( 2 k + 1 ) n = 1 ∑ k n 3 = ( 2 k ( k + 1 ) ) 2