Question

if 12 term of am ap is -13 and the sum of first four term is 24 what is the sum of 10 term​

Answer 1

Solution :

Let a be the first term and d be the commen difference

a_12 = -13

a+ (12 - 1)d = -13

a+ 11d =-13 ......(I)

Also, S_4= 24

4/2[2a + (4 - 1)d] = 24

2(2a+3d) = 24

2a + 3d = 12 ..........(ii)

From (1) and (ii), we get:

19d = -38

d = -2

Putting the value of d in (i), we get:

a + 11(-2) = -13

a =9

S_10 = 10/2 [2 x9 + (10 - 1)(-2)]

S_10 = 5[18 +9(-2)] = 0