1.

Find the sum of the following arithmetic progressions : a + b, a – b, a – 3b, … to 22 terms

Answer»

For the given AP the first term a is a + b, and common difference d is a difference of the second term and the first term, which is a - b - (a + b) = - 2b 

To find : the sum of given AP 

The formula for sum of AP is given by,

s = \(\frac{n}{2}\)(2a + (n-1)d

Substituting the values in the above formula,

s = \(\frac{22}{2}\)(2a + 2b + (21)(-2b))

s = 11(2a - 40b)



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