Question

fourth term of an ap is 13 and the tenth term is 31. find an ap and the sum of first of tenth terms and eighth ?

Answer 1

Answer:

Step-by-step explanation:

a4=13and a10 =31

a+3d=13 and a+9d=31

By solving equations

We get a=4 and d=3

A.p is 4,7,10,13......

Sum of 10 terms =10/2{2(4)+(10-1)3}

=5{8+27}

=5 (35)=175

a8 = a+7d=4+7×3=25

Answer 2

a4 =a+3d (1)
a10=a+9d. (2)
Subtract one and two
a+3d=13
a+9d=31
_________
6d=18. and d = 3
take equation no.1 a+3d=13=>a=13-3(3)=13-9=4
a=4. d=3
S ten =10/2{2*4+(10-1)3}. n/2[2a+(n-1)d
=5{8+27}
=5*35=>175//
a8=4+(8-1)3=>4+21=>25//