Question

find the sum of a+b,a-b,a-3b,.......upto 22 terms​

Answer 1

Answer:

So the formula for finding the sum is: Sn = n/2 * (2a+(n-1)*d)

Here a = a + b

n = 22

d = -2b since d = (a-b)-(a+b) that is if x,y,z... are in ap then the common difference d = y-x or z-y

Substituting all the values we get:

Sn = 22/2 * (2(a+b)+(22-1) * -2b)

= 11 * (2a + 2b +21 * -2b)

= 11 * (2a + 2b + -42b)

= 11 * (2a - 40b)

Sn = 22a - 440b

I hope this solution helped you :)

Answer 2

u want to write the formula

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