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Find a formula for each of the sums in Exercises 39, and then use these formulas to calculate each sum for n=100,500and 1000

∑k=1nk3-1n4

Short Answer

Expert verified

The formula of the given summation is n-1n2+3n+44n3.

The sum when n=100is 0.255024.0.255024

The sum when localid="1649224503901" n=500is localid="1649224506104"  0.251000992.

The sum whenlocalid="1649224508540" n=1000is 0.250500249.0.250500249.

Step by step solution

01

Given information

The given summation is ∑k=1nk3-1n4.

02

Determine the formula for the given summation. 

The sum can be written as:

∑k=1nk3-1n4=1n4∑k=1nk3-1=1n4∑k=1nk3-∑k=1n1=1n4n2(n+1)24-n=n-1n2+3n+44n3

03

Evaluate the sum for  n=100,500 and 1000

Substitute 100for nin n-1n2+3n+44n3.

localid="1649224281170" 100-11002+3100+441003=0.255024

Substitute 500for nin n-1n2+3n+44n3.

localid="1649224305780" 500-15002+3500+445003= 0.251000992

Substitute 1000for nin n-1n2+3n+44n3.

localid="1649224336994" 1000-110002+31000+4410003=0.250500249

04

Write the conclusion

The formula is n-1n2+3n+44n3.

The sum whenn=100,500and1000are 0.255024,0.251000992and 0.250500249.

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