SOLUTION: the sum of the fourth and twelfth term of an A.P is 120.what is the sum of the first 15 terms of the A.p
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Question 843209: the sum of the fourth and twelfth term of an A.P is 120.what is the sum of the first 15 terms of the A.p
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
an = a + (n - 1)d
a4 = a + 3d
a12 = a + 11d
120=2a+14d
S = ½(2a + (n-1)d)n
S = ½(2a + (14)d)15
S = ½(120)15
S=900
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