求和(1)(a-1)+(a²-2)+…+(an-n)(2)(2-3X5^-1)+(4-3X5^-2)+…+(2n-3X5^-n)(3)1+2x+3x^2+…+nx^(n-1)
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/04 07:35:19
![求和(1)(a-1)+(a²-2)+…+(an-n)(2)(2-3X5^-1)+(4-3X5^-2)+…+(2n-3X5^-n)(3)1+2x+3x^2+…+nx^(n-1)](/uploads/image/z/5492297-65-7.jpg?t=%E6%B1%82%E5%92%8C%EF%BC%881%EF%BC%89%EF%BC%88a-1%EF%BC%89%2B%EF%BC%88a%26%23178%3B-2%EF%BC%89%2B%E2%80%A6%2B%EF%BC%88an-n%EF%BC%89%EF%BC%882%EF%BC%89%EF%BC%882-3X5%5E-1%EF%BC%89%2B%EF%BC%884-3X5%5E-2%EF%BC%89%2B%E2%80%A6%2B%EF%BC%882n-3X5%5E-n%EF%BC%89%EF%BC%883%EF%BC%891%2B2x%2B3x%5E2%2B%E2%80%A6%2Bnx%5E%EF%BC%88n-1%EF%BC%89)
求和(1)(a-1)+(a²-2)+…+(an-n)(2)(2-3X5^-1)+(4-3X5^-2)+…+(2n-3X5^-n)(3)1+2x+3x^2+…+nx^(n-1)
求和(1)(a-1)+(a²-2)+…+(an-n)(2)(2-3X5^-1)+(4-3X5^-2)+…+(2n-3X5^-n)(3)1+2x+3x^2+…+nx^(n-1)
求和(1)(a-1)+(a²-2)+…+(an-n)(2)(2-3X5^-1)+(4-3X5^-2)+…+(2n-3X5^-n)(3)1+2x+3x^2+…+nx^(n-1)
(1)可以把括号拆开,a有关写一起~等比数列q=a.数字写一起等差数列d=-1 (2)可以把括号拆开,数字写一起~等差数列d=2.带n的写一起~提取3等比数列5^n公比为1/5
第一问把a放一边加,123456789...放一边加,然后用等差,等比数列公式,第二问也是差不多。第三问要用到数列求和方法中的错位相减法