Question

Cho A = 1² + 2² + 3² + ... + 15² và B = 1.2 + 2.3 + ⋯ + 14.15. Khi đó B - A =

Answer 1

B-A=1.(2-1)+2.(3-2)+...+15(15-14)=1+2+..+15=16.15/2=120

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