Solving Sequence Math Problems: Finding d and U1 | Helpful Tips and Tricks

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Homework Help Overview

The discussion revolves around a sequence math problem involving the terms and sum of a sequence, specifically focusing on finding the common difference (d) and the first term (U1) given certain values.

Discussion Character

  • Exploratory, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss setting up simultaneous equations based on the given information about the sequence. There is an exploration of how to express the first term and common difference in terms of each other.

Discussion Status

Some participants have provided equations derived from the problem's conditions, and there is an indication of progress towards finding the values of d and U1. However, the discussion does not reach a consensus on the final values, and further exploration is implied.

Contextual Notes

Participants are working with specific values for the sequence and are constrained by the need to derive terms from the equations set up based on the sum and specific term provided.

IB
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Please help...

Given U3 = 0
S15 = -300
How can you find d? And U1?

(Instead of "T", we use "U" for "term", and d is the common difference)

Thanks!
 
Last edited:
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No one can solve this problem? :(
 
two simultaneous equations.
one equation for each information given.
solve the equations for a and d.
 
Thanks a lot!
 
Set up the 2 equations:

Sn = n/2[2a + (n-1)d]
Un = a + (n-1)d

Substitute known values:

-300 = 15/2 [2a + (15-1)d]
-40 = 2a + 14d
-40 - 14d = 2a
a = -20 - 7d

0 = a + (3-1)d
0 = a + 2d
a = -2d

Set them equal to each other and solve:

-20 - 7d = -2d
-20 = 5d
d = -4

there's your d value bro...i'm sure you can do the rest! :approve:
 
Yup, my bro's so smart! :smile:
 

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