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If the sum of 1st M terms of an AP is m....

If the sum of 1st M terms of an AP is m. and the sum of 1st N terms is n, show that- the 1st term of this AP is `(mN(N-1)-nM(M-1))/(MN(N-M))`

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UNITED BOOK HOUSE-MODEL QUESTION PAPERS-SET 7-EXERCISE
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