Whoa!!Solve this without a calculator!!-2

Algebra Level 2

What is the sum of cubes of the first 10 positive integers?


The answer is 3025.

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3 solutions

Caleb Townsend
Mar 16, 2015

There is a super fast way to solve this if you know the identity k = 1 n k 3 = ( T n ) 2 \sum_{k=1}^n k^3 = (T_n)^2 where T n T_n is the n n th triangular number. Substitute n = 10. n=10. k = 1 10 k 3 = ( T 10 ) 2 = 5 5 2 = 3025 \sum_{k=1}^{10} k^3 = (T_{10})^2 = 55^2 \\ = \boxed{3025}

Shubham Dwivedi
Dec 6, 2014

Answer must be 2025 not 3025 as first 10 whole numbers will be 0,1,2,3,4,5,6,7,8,9

Oh sorry! The question meant to be The first 10 natural numbers. Thnx for telling it. I will get it fixed

Mehul Arora - 6 years, 6 months ago

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I have updated the phrase to "positive integers" instead. In some countries, natural numbers include 0.

Calvin Lin Staff - 6 years, 6 months ago

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Oh! Thanks Sir!

Mehul Arora - 6 years, 6 months ago
Mehul Arora
Dec 6, 2014

We can solve this problem with the help of a generalized formula which says that the sum of the cubes of the first n numbers is

([n(n+1)]/2) ^2

Thus the required answer is [(10X11)/2]^2 =3025

Note that 0 is also a whole number!!! So the first 10 whole numbers would be 0, 1, ,2 ,3 ,4 ,5 ,6 ,7 ,8 and 9. Your question didn't say that the first 10 COUNTING numbers. It just said that the first 10 WHOLE numbers so 0 should be included and the answer should be 2025

Joshua Omar Pestaño - 6 years, 6 months ago

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Oh sorry! The question meant to be The first 10 natural numbers. Thnx for telling it. I will get it fixed.

Mehul Arora - 6 years, 6 months ago

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