Question

Q. The first and the last terms of an AP are 10 and 361 respectively. If its common difference is 9 then find the number of terms and their total sum?​

Answer 1

Answer:

Number of terms= 40

Step-by-step explanation:

a= 10

an= 361

d= 9

We know that,

an= a+(n-1)d

=>361= 10 + (n-1)9

=>361= 10 + 9n - 9

=>361-10+9= 9n

=>360 = 9n

=>n = 40

Answer 2

Step-by-step explanation:

.t1=10., tn=361, a = 10,d=9

n = ( t n-t1)/d+1=(361-I0)/9 +1=40

Number of terms=40. Ans

Sum Sn=n/2{2a+(n-1)d}

= 40/2{2x10+(40-1)9 }

=20{20+351}

=20x371=7420. .... Ans