Summing an Arithmetic Progression

Algebra Level 1

The formula for the sum of the first n n terms of an arithmetic progression is given by S n = n ( 2 a 1 + ( n − 1 ) d ) 2 S_n = \dfrac{n(2a_1 + (n-1)d)}2 .

Find the sum of the first 6 terms when a 1 = − 2 a_1 =-2 and d = 3 d= 3 .

18 33 23 48

View wiki
Hill Taeudomkul by Hill Taeudomkul , 19, Thailand

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Ralph James
Mar 14, 2016

S 6 = 6 ( 2 ⋅ − 2 ) + ( 6 − 1 ) 3 ) 2 = 3 ⋅ ( − 4 + 15 ) = 3 ⋅ 11 = 33 \ S_6 = \dfrac{6(2 \cdot -2) + (6 - 1)3)}{2} = 3 \cdot (-4 + 15) = 3 \cdot 11 = \boxed{33}

0 Helpful 0 Interesting 0 Brilliant 0 Confused

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...