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## What is the common difference of an A.P. in which a21 – a7 = 84? Mathematics CBSE class 10 2017

What is the common difference of an A.P. in which a21 – a7 = 84?By:tarun101

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## Answers

We know aₙ = a₁ + (n-1)d

Thus a₂₁ = a₁ + 20d

and a₇ = a₁ + 6d

Thus a₂₁ - a₇ = (a₁ + 20d) - (a₁ + 6d)

= 14d

According to question a₂₁ - a₇ = 84

∴ 14d = 84

or, d = 6

Thus the common difference is 6.

akialwayz

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