S5=5*（a1+a5）/2=10
a5=8 a1=-4
公差d=(a5-a1）/4=3
所以等差数列通项为an=-4+3（n-1）=3n-7 a10=23
s10=10*（a1+a10）/2=10*（-4+23）/2=95