等比数列,等差数列奇数项和偶数项的公式.

题目

等比数列,等差数列奇数项和偶数项的公式.

答案

设原数列首项为a,公差为d,原数列依次为a,a+d,a+2d,a+3d,.,a+2nd奇数项为：a,a+2d,a+4d,.,a+2nd奇数项和：S奇 = [a + (a+2nd)](n+1)/2 = (a+nd)(n+1)偶数项为：a+d,a+3d,a+5d,.,a+(2n-1)d偶数项和：S偶 = [(a+d) + (a...