Find the sum of the first 10 terms of each arithmetic sequen

Find the sum of the first 10 terms of each arithmetic sequence. 33. a_1 = 8, d = 3 34. a_1 = -9, d = 4 35. a_3 = 5, a_4 = 8 36. a_2 = 9, a_4 = 13

36. a2 = 9 ; a4 = 13

n the term of A.P. : an = a1 +(n-1)d

2nd term : 9 = a1 + d

4rth term : 13 = a1 +3d

solve the two equations to get a1, d:

2d = 4 ---> d=2

a1 = 9 -2 =7

So, Sum of n terms = (n/2)[2a +(n-1)d]

Sum of 10 terms = (10/2)[ 2*7 +9*2]

= 5[ 14 +18]

= 160