Questions
If the first, second and last terms of an A.P. are a, b and 2a respectively, then its sum is
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a
ab2(b−a)
b
abb−a
c
3ab2(b−a)
d
None of these
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Correct option is C
Here a1 = a and a2 = b∴Common difference d = a2 – a1 = b – aLet n be the number of terms in the series∴ an=2a=a+(n−1)d or (n−1)d=a or (n−1)(b−a)=a∴ n−1=ab−a or n=ab−a+1=a+b−ab−a=bb−a∴ Sum =n2a1+an=b2(b−a)(a+2a)=3ab2(b−a).Similar Questions
If and 1 are in A.P, then x is equal to
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