Question

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

Answer 1

no ans me
mote asibani

Answer 2

a+(n-1)d=nth term

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

sum of n terms = n/2(2a+(n-1)d)

4/2(2a+3d)=24

4a+6d=24 ...................(2nd equation)

4a+6d=24

a+11d=-13           (multiply 4 on both sides)

4a+44d=52 .......................(3rd equation)

subtract 1 from 3

4a+44d=52

4a+6d=24

(44-6)d=28

38d=28

d=28/38

a+11d=-13

a+11(28/38)=-13

a=-13*38/11*28

a=1257

5(2514+9(28/38)

approxiamately 12,603