Question

Find the sum of ap 5+11+17+........​16 th terms

Answer 1

$AP : 5 , 11 , 17 , .....\\\\a = 5 \\\\d = 11 - 5 = 6\\\\n = 16$

$S_n=\frac{n}{2}[2a+(n-1)d]\\\\S_n=\frac{16}{2}[10+(16-1)6]\\\\S_n=8[10+90]\\\\S_n=8[100]\\\\S_n=800$

Answer 2

Answer:

Sum of apap 5+11+17+........​16 th term is 816

Step-by-step explanation:

a = 5 , d = 6, nth = 16, to find an = ?

we konw that , an = a + (n-1)*d

so, an = 5 + 15*6

an = 5+90

an = 95

now , Sn = ?

Sn= n/2 (2a +  (n -1 )d)

Sn = 16/2 (12 + (16 - 1) * 6)

Sn = 8(12+ 90)

Sn = 8(102)

Sn = 816