Sequence anc Series (1 Viewer)

[kevda1st]

This was in my test and i couldn't do it...

1 , 3, 6, 10 and 15 are triangular numbers..

Use the sum of an arithmetic series to find the 30th term

 

[Timothy.Siu]

This was in my test and i couldn't do it...

1 , 3, 6, 10 and 15 are triangular numbers..

Use the sum of an arithmetic series to find the 30th term

T1=1
T2=1+2=3
T3=1+2+3=6
T4=1+2+3+4=10
T30=1+2+3+.....+30
well T30=(1+30)/2 x30=465

 

[AlexJB]

He posted above the correct answer. If you don't understand it though, he just examed T30, saw it was 1+2+3+...+30, which in turn is the sum of an arithmetic progression with starting value 1, final value 30, difference 1, n=30.

Sn = (n/2)(a+l)
S30 = (30/2)(1+30) = 15x31 = 475