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

Posted by Soniya Rana 5 years, 1 month ago

CBSE > Class 10 > Mathematics

3 answers

Open Beast 5 years, 1 month ago

a21 = a + 20d a7 = a + 6d ATQ, a21-a7=84 a+20d-(a+6d) = 84 a - a + 20d - 6d = 84 14d = 84 d = 84/14 d = 6.

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Vandana 🇮🇳 5 years, 1 month ago

a21-a7=84 (a+(n-1) d) - (a+(n-1)d)=84 We 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)=84 a+20d-a-6d=84 Sign change because i have open the bracket and a got cancel as opposite sign. 20d-6d=84 14d=84 d=84÷14 d=6 So 6 is the answer.

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Tanu Man 5 years, 1 month ago

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CBSE > Class 10 > Mathematics