Question

if 12th term of an ap is -13 and the sum of first four terms is 24 what is the sum of first 10 terms

Answer 1

Step-by-step explanation:

tn=-13 TN=a+(n-1)d

a+11d=-13....(1)

S4=24. Sn=1/2n[2a+(n-1)d]

1/2*4[2a+3d]=24

1/8(2a+3d)=24

2a+3d=192......(2)

solve 1, 2 we got a and d

substitute a and d in

S10=1/2*10(2a+9d)