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The twelfth term of alinear sequence is 47 and the sum of The first 3 terms is 21 find the sum of the first 15 terms of the sequence
3 years ago

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R_scott
a + 11 d = 47 ... 3 a + 33 d =141

3 a + 2 d = 21

subtracting equations (to eliminate a) ... 31 d = 120

find a and d

plug into the sum formula


f y i ... it seems like there may be an incorrect value in the problem
3 years ago

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