Question

Which expression defines the given series for seven terms?

8 + 13 + 18 + . . .

Answer 1

The given question is 8+13+18+...... which is in arithmetic progression . And for arithmetic series, we have to use the following formula for nth term .

`a_(n) = a + (n-1)d`

Here a =8 , d=5

So we get

`a_(n) = 8+(n-1)5 = 5n +3`

And the required expression for n=7 is

`\sum_(n=1)^(7)(5n+3)`