SOLUTION: An arithmetic sequence has first term a and common difference d. The sum of the first 25
terms is 15 times the sum of the first 4 terms.
a) Find a in terms of d.
b) Find the 55t
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Question 1186962: An arithmetic sequence has first term a and common difference d. The sum of the first 25
terms is 15 times the sum of the first 4 terms.
a) Find a in terms of d.
b) Find the 55th term in terms of a.
Found 2 solutions by greenestamps, MathLover1:
Answer by greenestamps(13198) (Show Source): You can put this solution on YOUR website!
a)
S(4) = (a)+(a+d)+(a+2d)+(a+3d) = 4a+(1+2+3)d = 4a+6d
S(25) = (a)+(a+d)+(a+2d)+...+(a+23d)+(a+24d) = 25a+(1+2+...+23+24)d = 25a+300d
S(25) is 15 times S(4):
b)
Answer by MathLover1(20849) (Show Source): You can put this solution on YOUR website!
a) Find a in terms of d
Sum of terms :
For terms
For terms
given that the sum of the first terms is times the sum of the first terms, so e have
b) Find the th term in terms of
=>
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