Question

If the nth term of a sequence is 5+2n, then find the sum of first 20 terms.
Pls answer fast

Answer 1

Answer:

Step-by-step explanation:

First term = 5+2*1=7

Second term= 5+2*2=9

20th term= 5+2*20= 45

Therefore sum,

Sn=n(a+l)/2

= 10*(5+45)

=500

Answer 2

Answer:

The sum of first 20 terms is 520

Step-by-step explanation:

• nth tern of the given sequence is 5+2n
• putting n=1,

we get the 1st term = 5+2.1=5+2=7

• putting n=2,

we get the 2nd term =5+2.2=5+4=9

• putting n=3,

we get the 3rd term = 5+ 2.3 =11

...........

• putting n = 20,

we get the 20th term = 5+ 2.20= 45

• hence the series goes like

7,9,11,13,15,.......45

• To find the sum S of the first n terms of an arithmetic sequence we can use the formula,

S=n(a1 + an)/2

where n is the number of terms in the series , a1 is

the first term and an is the last term.

• using the above formula we can calculate the sum S of first 20 terms of the given series like this:

S= 20(7+45)/2 = 20×52/2=520