Question

write the sum of first 10 terms of A.P 15,10,5,​

Answer 1

Answer:

The sum of first 10 terms of A.P 15,10,5,... is (-75)

Step-by-step explanation:

Answer 2

Answer:

-75 is the sum of 1st 10 terms of the AP.

Step-by-step explanation:

The Arithmetic sequence is: 15,10,5,..

First-term (a)=15.

Common difference (d) = 10-15= 5-10= -5

Let no.of terms(n) be 10.

aₙ=a+(n-1)d

a₁₀=15+(10-1)(-5)

    = 15 + (9*-5)

    = 15-45

    = -30

Sum of n terms of an AP (Sₙ) = n/2 (2a+(n-1)d)

We have the 1st term and the last term. So, the equation still reduces to:

n/2(a+l) where a is the 1st term and l is the last term of the AP.

S₁₀ = 10/2 (15+(-30))

     = 5×-15

     = -75