Question

Find the sum of first 20 terms of the A.P. 3,3,3,3,.....

Answer 1

Answer:

First term, a = 3

Last term, L= 57

nth term, nth= 20

Formula for the sum of 20 term

Sn=n/2{a+L}

Put the values

S20= 10{3+57}

S20=10.60

S20= 600 Answer.

Answer 2

Given,

• A.P = 3, 3, 3, 3, ...

• First Term (a) = 3

• Common Difference (d) = 2nd term - 1st term = 3 - 3 = 0

• Number of Terms (n) = 20

The equation to find the sum of first n terms is,

$\boxed{\bf S_n=\dfrac{n}{2}[2a+(n-1)d]}$

Applying the values to the equation,

$\implies\sf S_n=\dfrac{20}{2}[(2\times 3)+(20-1)0]$

$\implies\sf S_n=10[6+0]$

$\implies\sf S_n=10\times 6$

$\bold{\implies\sf S_n=60}$

Therefore,

$\huge\boxed{\bf Sum \:of \:first \:20 \:terms=60}$