1.

s0AP in21

Answer»

For an AP nth term isan = a + (n-1)d

Where, a = first term and d = common difference

Given,a21 - a7 = 84(a + 20d) - (a + 6d) = 8420d - 6d = 8414d = 84d = 84/14 = 6

Therefore, common difference= 6



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