A few days ago
Anonymous

Solve using substitution?

7. Suppose for an arithmetic sequence t4 = 2 and t40 = -106. Find the equation for the nth term.

-Arithmetic formula: tn = t1 + (n-1)d

2 = t1 + (4-1)d

2 = t1 + 4d – d

2 = t1 + 3d

2 – 3d = t1

-106 = t1 + (40-1)d

-106 = t1 + 40d – d

-106 = t1 + 39d

-106 – 39d = t1

t1 = -106 – 39d

t1 = 2 – 3d

Solve by substitution?

Thanks in advance,

Top 1 Answers
A few days ago
Anonymous

Favorite Answer

t1 = -106 – 39d …(1)

t1 = 2 – 3d …(2)

Substitute for t1 from the first equation in the second. In other words, equate the right hand sides, as they are both equal to t1.

2 – 3d = -106 – 39d

36d = -108

d = -108 / 36 = -3.

Putting this value in (2):

t1 = 2 – (-9) = 11.

Hence the n-th term is:

tn = 11 – 3(n – 1).

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