[birgül sabri]

10

∑

k=4

k³=?

[Alp]

n

∑

k=1

k³= [n(n+1)/2]²

10

∑

k=4

k³=

10

∑

k=1

k³-

3

∑

k=1

k³

10

∑

k=1

k³= (10.11/2)²= 3025

3

∑

k=1

k³=(3.4/2)²⁼³⁶

3025-36=2989