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# Sequences and Series

-1
353
7 pls help ;-;

May 20, 2021

#1
+1

https://web2.0calc.com/questions/i-am-having-trouble-with-this-question-on-a-semester-review

See if you can figure it out from this problem.

We need the starting term (a_1) and we to know how much you increase/decrease from term to term.

=^._.^=

May 20, 2021
#2
+1

I was having trouble on how to find the common ratio. at first i was thinking as taht i needed to treat a_4 like a problem such as a_2=41 therefore 41=a_1*r but i can't figure out how to format it that way or if im even on the right path.

Guest May 20, 2021
#3
0

wait so 41=a_1 r^3
ans 125=a_1  r^15

Guest May 20, 2021
#4
+1

i went to 125=41r^12 but now im stuck. pls help ;-;

Guest May 20, 2021
#5
+2

You're solving for geometric, not arithmetic.

First, we need to look for the common ratio.

x, x + y, x + 2y, x + 3y, x + 4y, ...

a_4 = x + 3y

a_16 = x + 15y

Subtract those 2 equations.

125-41 = x + 15y - (x + 3y)

84 = 12y

y = 7 (that's the common ratio)

a_4 = x + 3y

41 = x + 3(7)

x = 20

So our first term is 20, then we add 7 for the next term.

a_n = 20 + 7(n-1)

=^._.^=

catmg  May 20, 2021
#6
0

Yeah i realized taht a while ago lol. I got the same answer! pog

Guest May 20, 2021
#7
+1

Nice. :))

=^._.^=

catmg  May 20, 2021