Question

The 4th term of an arithmetic sequence is 12 and the 8th term is 36. Find the 17th term of the sequence.

Answer 1

Answer: 90

Step-by-step explanation:

The formula for calculating the nth term of a sequence is given as :

$t_{n}$ = a + ( n - d )

Where a is the first term

d is the common difference and

n is the number of terms

This means that the 4th term of an arithmetic sequence will have the formula :

$t_{4}$ = a + 3d

And the 4th term has been given to be , 12 ,substituting into the formula we have

12 = a + 3d .............................. equation 1

Also substituting for the 8th term , we have

36 = a + 7d .............................. equation 2

Combining the two equations , we have

a + 3d = 12  ................... equation 1

a + 7d = 36 ------------ equation 2

Solving the system of linear equation by substitution method , make a the subject of formula from equation 1 , that is

a = 12 - 3d ................... equation 3

substitute a = 12 - 3d into equation  2 , equation 2 then becomes

12 - 3d + 7d = 36

12 + 4d = 36

subtract 12 from both sides

4d = 36 - 12

4d = 24

divide through by 4

d = 6

substitute d = 6 into equation 3 to find the value of a, we have

a = 12 - 3d

a = 12 - 3 ( 6)

a = 12 - 18

a = -6

Therefore , the 17th term of the sequence will be :

$t_{17}$ = a + 16d

$t_{17}$ = -6 + 16 (6)

$t_{17}$ = -6 + 96

$t_{17}$ = 90

Therefore : the 17th term of the sequence is 90