aswer this question
find the comman difference
a21-a7=84
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21a - 7a = 84
14a = 84
a = 84/14
a = 6
14a = 84
a = 84/14
a = 6
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a21 can be written as a + 20d
a7 can be written as a + 6d
where a is first term
d is common difference
=> because an = a + ( n - 1 )d
a21 - a7 = 84
a + 20d - ( a + 6d ) = 84
a + 20d - a - 6d = 84
14d = 84
d = 6
a7 can be written as a + 6d
where a is first term
d is common difference
=> because an = a + ( n - 1 )d
a21 - a7 = 84
a + 20d - ( a + 6d ) = 84
a + 20d - a - 6d = 84
14d = 84
d = 6
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