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arithmetic sequence?
The eleventh term of an arithmetic sequence is 30 and the sum of the first eleven terms is 55. What is the common difference? d=5 Hint: use the sum formula. Note that the last term is already given to you!
I keep getting 1
1 Answer
- EfreniloLv 45 years agoFavorite Answer
a(11) = 30 = a1 +d(11-1)
a1+10d = 30 eq.1
S(11) = (11/2)*(2a1 +d(11-1)) =55
(11/2)*(2a1+10d) = 55
Multiply by 2 both sides and simplifying,
22a1 + 110d = 110 eq.2
Solving eq. 1 and 2 gives
a1 = -20
d= 5
