Question

if the nth term is 3-2n.find the sum of fifteen terms​

Answer 1

answer: -270

explanation:

•Find a and l(last term-15) and n=15(given)

•substitute these values in the formula-

Sn=n/2(a+l)

thats it!!!

Answer 2

The sum of the fifteen terms is $-195$

Step by step explanation:

Given: The nth term is $3-2n$

To find: The sum of fifteen terms of given sequence

Formula used:  $s_{n} =\frac{n}{2} (a+1)$

Here we know that,

$a_{n} =3-2n$

Taking $n=1$,

$t_{n} =3-2n$

$t_{n} =3-2(1)$

$t_{1} =1$

Now take $n=15$

⇒3-30

⇒-27

$s_{n} =\frac{n}{2} (a+1)$

$s_{15}= \frac{15}{2} [1+(-27)]$

$=\frac{15}{2} [-26]$

$=15*(-13)$

$=-195$

Therefore the fifteen term of the sequence is $s_{15} = -195$