Question

The sum of the first six terms of an AP is 120.If the forth term is 23 ,find the first term and the common dinference.​

Answer 1

30

Explanation:

The AP is 5,11,17,23,29,35

So, the difference is 35-5 = 30

Answer 2

S6=120

S6=6/2[2a+(n-1)d]

=3(2a+5d)

120 =6a+15d --------(1)

a4=23 = a+3d

=> 23-3d=a--------(2)

substitute value of a in (1)

u get values of a and d

Explanation: