Question:
A21-a7=84 find common difference
Answer:
Let a is the first term and d is the common difference of the AP
Now, we know that an = a + (n - 1)d
Given, a21 - a7 = 84
=> {a + (21 - 1)d} - {a + (7 - 1)d} = 84
=> a + 20d - a - 6d = 84
=> 14d = 84
=> d = 84/14
=> d = 6
So, the common difference of the AP is 6
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