Question

If nth term of a.p is given by (-4x+15) . Find the sum of first 20 terms of this a.p

Answer 1

Answer:

Step-by-step explanation: first find the first term by putting 1 in nth term of A.P ie (-4×1+15)=11

Now find 20th term ie (-4×20+15)=-65

Now using sum formula of A.P ie S=n/2(a+l) where n represents no of terms for addition ,a=first term and l= last term

S=20/2(11-65)

S=10(-54)

S=-540