Question

数学解答题？

数学解答题

Answer 1

an=a1+(n-1)d
a3+a5=16
2a1+6d=16
a1+3d=8 (1)
a7=17
a1+6d=17 (2)
(2)-(1)
3d=9
d=3
from (1)
a1+3d=8
a1+9=8
a1=-1
an =-1+3(n-1) = 3n-4
S10
=a1+a2+...+a10
=5(2a1+9d)
=5(-2+27)
=125

Answer 2

an=a1+(n-1)d
a3+a5=16
2a1+6d=16
a1+3d=8 (1)
a7=17
a1+6d=17 (2)
(2)-(1)
3d=9
d=3
from (1)
a1+3d=8
a1+9=8
a1=-1
an =-1+3(n-1) = 3n-4
S10
=a1+a2+...+a10
=5(2a1+9d)
=5(-2+27)
=125

Answer 3

1.因为a3+a5=16，a7=17.所以2a1+6d=16，a1+6d=17.所以a1=-1，d=3
2.由1得an=3n-1，s10=10x(-1)+10ⅹ(10-1)/2X3=125