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91Ó°ÊÓ

Find the sum or quantity without completely expanding or calculating any sums.

Given∑k=025k=325and∑k=328k-32=14,910, find the value of∑k=325k2-5k+9.

Short Answer

Expert verified

The sum is13,502

Step by step solution

01

Step 1. Given information

∑k=025k=325

∑k=328k-32=14,910

02

Step 2. Rewrite the sum:

∑k=325k2-5k+9=∑k=325k2-6k+k+9=∑k=325k2-6k+9+k=∑k=325(k-3)2+k=∑k=325k-32+∑kk=325

03

Step 3. To find ∑k=325k

∑k=025k=3250+1+2+∑k=325k=3253+∑kk=325=325∑kk=325=325-3∑kk=325=322

04

Step 4. To find ∑k=325k-32

∑k=328k-32=14,910∑k=325k-32+(26-3)2+(27-3)2+(28-3)2=14,910∑k=325k-32+(23)2+(24)2+(25)2=14,910∑k=325k-32+529+576+625=14,910∑k=325k-32+1730=14,910∑k=325k-32=14,910-1730∑k=325k-32=13,180

05

Step 5. Substitute the value of the sum obtained in steps 3 and 4 into step 2.

∑k=325k2-5k+9=∑k=325k-32+∑k=325k=13180+322=13502

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