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If common difference of an AP is 3 then,a20 - a25 = ? |
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Answer» a = 1st termd = 3then a20\xa0= a + (20 - 1) d = a + 19x3= a + 57 ......... i a\xa025 = a + 24 d = a + 24 x 3 = a + 72 ............................ ii as per question i - ii a20\xa0\xa0- a25 = a + 57 - a - 72 = - 15 Let first term of an A.P. is a and common difference is d.Given common difference =3 d=3Now a20-a25=a+(20-1)d -(a+(25-1)d) [by using an=a+(n-1)d] =a+19d -(a + 24d) =a+19d - a -24d =-5d =-5×3 (since d=3 given) = -15 |
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