Question

Find the number
of terms in an AP. 18, 15, 12,...,-48
and also find the sum of all of its terms.​

Answer 1

Answer:

number of terms = 21

Sum of AP = -315

Step-by-step explanation:

We know, tₙ = a + (n-1) * d

so,     -48 = 18 + (n-1) * 3

         -66 = (n-1) * 3

         -22 = n-1

          n = -21

Since no. of terms cannot be negative so n = 21

Now Sum of all terms = n/2*[first term + last term] = -21/2*[18-48]  

                                                                                   = -21 * 15 = -315

I hope this helps you