In the arithmetic sequence {an}, if A4 + A8 = 16, then A2 + a10=______ ．

In the arithmetic sequence {an}, if A4 + A8 = 16, then A2 + a10=______ ．

∵ the sequence {an} is an arithmetic sequence, and A4 + A8 = 16. According to the properties of arithmetic sequence, A2 + A10 = A4 + A8 = 16

In the known arithmetic sequence {an}, A2 = 7, A4 = 15, then the first 10 terms and S10=
It's better to explain the process of solving the problem in detail. Thank you in advance!

According to the meaning of the title, A2 = a1 + D = 7
a7=a1+3d=15
We can get A1 = 3
d=4
According to the sum formula of the first n terms of the arithmetic sequence, S10 = 10A1 + [10 * (10-1) / 2] * d = 10 * 3 + [10 * (10-1) / 2] * 4 = 210

Cubic power of X + cubic power of y = 19, x + y = 1, square of X + square of Y=

x³+y³=（x+y）（x²-xy+y²）=x²-xy+y²=19
（x+y)²=x²+2xy+y²=1
∴xy＝﹣6
∴x²＋y²＝19－6＝13