四棱柱ABCD-A1B1C1D1的底面ABCD为矩形,AB=1,AD=2,AA1=3,角A1AB=角A1AD=60度,求AC1.

问题描述:

四棱柱ABCD-A1B1C1D1的底面ABCD为矩形,AB=1,AD=2,AA1=3,角A1AB=角A1AD=60度,求AC1.
2.设数列{an }前n 项和Sn =n^2,n8=?

AC1=根号下(1.5^2+2.5^2+(根号下0.5)^2)=3
a8=s8-s7=15