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hey743358
25.06.2019 •
Mathematics
Find n for a series for which a1= 30, d = -4, and sn = -210. a. -21 b. 21 c. -10 d. 10 select the best answer from the choices provided a) a b) b c) c d) d
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Ответ:
n= 21 option B
Step-by-step explanation:
a1= 30, d = -4, and Sn = -210
WE use sum formula
we are given with a1 and d so its arithmetic sequence
the sum formula for arithmetic sequence is
a1= 30 and d= -4 sn =-210
Plug in the values and solve for n
Now distribute the fraction n/2
-210 = 32n - 2n^2
we add 210 on both sides
-2n^2 +32n +210=0
Divide whole equation by -2
Now we factor left hand side
Product is -105 and sum is -16
-21 times (5) = -105
-21 + (5) = -16
(n-21) (n+5)=0
n -21 = 0 so n= 21
n +5 =0 so n = -5
number of terms cannot be negative so n= 21
Ответ:
im assuming you mean 3 times
Step-by-step explanation:
it would be =
pam = p
bill = b
p=3b