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X, X+1,X-1are three terms of ap,its sum up to 20 terms is |
Answer» solution:-given TERMS given are not in proper way and also it not mentioned that these are first three terms are not.anyway in proper way these are, given bellow first TERM= X-1 second term= X third term= X+1 thus common difference (d)= X-(X-1) = 1 Sum upto 20 terms(S20) formula USED:- An= (n/2) [ 2a+(n-1) d] = (20/2)[ 2(X-1)+(20-1) ×1] = 10[ 2X-2+19] = 20X+170 |
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