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花朵
共回答了12个问题采纳率:100% 举报
求和(a-1)+(a^2-2)+……+(a^n-n)
(a-1)+(a^2-2)+……+(a^n-n)
=a+a^2+.+a^n-(1+2+...+n)
=(1-a^(n+1))/(1-a)-n(n+1)/2
2.sin^2 0°+sin^2 1°+……+sin^2 89°+sin^2 90°
=(sin^2 0°+sin^2 90°)+(sin^2 1°+sin^2 89°)+.+sin^2 45°(共45个1)
=1+1+.+1/2(共45个1)
=45.5
sin^2 a+sin^2 (90°-a)=1
原式=sin^2 0°+sin^2 90°+sin^2 1°+sin^2 89°+……+sin^2 45°=45+0.5=45.5
1年前
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