Question

first term and common difference of an A.P. are 6 and 3 respectively. find S15​

Answer 1

Given: The First term of an A.P.(a) is 6

            The common difference of the A.P.(d) is 3

To find: The value of S15

Solution: An Arithmetic Progression(A.P.) is a sequence or a series of numbers that have a common difference of a constant value. In solving this numerical, we have to implement the sum of A.P. of the nth term.

      a=6 and d=3

We know that,

             Sum of an A.P. of nth term, Sn=n/2{2a+(n-1)d}

∴S15 =15/2{2×(6)+(15-1)×3}

        =15/2{12+14×3}

        =15/2{12+42}

        =(15/2)×54

        =7.5×54

        =405

Hence, S15=405