Question

Find the 16th term of AP. 7,11,15,19,.......find the sum of first 6 terms

Answer 1

a=7
d=11-7=4
16th term =a+15d
=7+15×4
=7+60=67
16th term=67
6th term=7+5×4
=7+20=27
sum of 1st 6term =n/2(a+l)
6/2(7+27)
=3×34=102

Answer 2

Answer:

The sum of first 6 terms is 117 and 16th term is 67

Step-by-step explanation:

A.P.= 7,11,15,19,.......

Fist term =a = 7

Common difference =d = 11-7=15-11= 4

Formula of nth term in A.P. =   $a_n=a+(n-1)d$

So, for 16th term put n = 16

$a_{16}=7+(16-1)4$

$a_{16}=7+(15)4$

$a_{16}=7+60$

$a_{16}=67$

Sum of n terms : $\frac{n}{2}(2a+(n-1)d)$

So, sum of first 6 terms =  $\frac{6}{2}(2(7)+(6-1)5)$

                                       =  $3(14+25)$    

                                       =  $3(39)$    

                                       =  $117$    

Hence the sum of first 6 terms is 117 and 16th term is 67