Question

Is part A correct? Im not entirely sure about it and also what is part B???

Answer 1

Answer:

see explanation

Step-by-step explanation:

A

Given

$S_{n}$ = $\frac{1}{2}$(n² + n) ← multiply each term in the parenthesis by $\frac{1}{2}$

    = $\frac{1}{2}$ n² + $\frac{1}{2}$ n

B

To find the sum of the first 12 whole numbers, substitute n = 12 into the formula, that is

$S_{12}$ = $\frac{1}{2}$ (12² + 12) = $\frac{1}{2}$ (144 + 12) = $\frac{1}{2}$ × 156 = 78

Answer 2

Answer:

A) $\frac{n^2}{2} + \frac{n}{2}$

B) 78

Step-by-step explanation:

B) To find the sum of first 'n' whole numbers , formula used is :-

$\frac{1}{2} ( n^2 + n)$

We have to find the sum of first 12 whole numbers . So here n = 12

Putting the value of 'n' in above formula ,

$\frac{1}{2} ( 12^2 + 12) \\\\=> \frac{1}{2} ( 144 + 12)\\\\=> \frac{156}{2} = 78$