Question

In an AP, if the common difference (d)=-4 and the seventh term (T7) is 4 , then find the first term (a).

Answer 1

a+6d=4
a+6×-4=4
a-24=4
a=28

Answer 2

an=a+(n-1)d

Solution :
a7=a+(7-1)*-4
a7=a+6*-4
a7=a-24
Hence, d=(-4)
a-24=4
a=28
So, a=28