what is the common difference of an a.p. in which a 21 -a 7 =84 .

1.	what is the common difference of an a.p. in which a 21 -a 7 =84 .
Answer» a21 = a + 20da7 = a + 6d ATQ,a21-a7=84a+20d-(a+6d) = 84a - a + 20d - 6d = 8414d = 84d = 84/14d = 6. a21-a7=84(a+(n-1) d) - (a+(n-1)d)=84We know the value of n and a and d is common.Soo..(a+(21-1)d) - (a+(7-1)d)=84(a+20d) - (a+6d)=84a+20d-a-6d=84Sign change because i have open the bracket and a got cancel as opposite sign.20d-6d=8414d=84d=84÷14d=6So 6 is the answer. Your question is not cleared

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