Question

28: nth of an A.P. is 4 and common difference is 2 at the sum of n terms is (-14) then (A) First term of the A.P​

Answer 1

Answer:

nth term is 4

a+(n-1)d=4

a+(n-1)2=4 ,as d=4 given

a+2n-2=4

a+2n=6

a=6-2n

the sum of n terns is

n/2[2a+(n-1)2]= -14

n(a+n-1)= -14

as we know a value substitute it in this equation

n(6-2n+n-1)= -14

n(5-n)= -14

n^2-5n-14=0

factorise it

n^2-7n-5n-14=0

n(n-7)+2(n-7)=0

(n-7)(n-2)=0

n=7 or n=-2

then the value of a is

10 or-8

hope it helps u

Explanation: