Predicting What Comes Next: Sequences and Progressions | Exercise 8.1

Question 1

Find the first five terms of the sequence in which the nthn^{\text{th}} term is given by, for n1n \ge 1:

(i) tn=3n4t_n = 3n - 4

(ii) tn=25nt_n = 2 - 5n

(iii) tn=n22n+3t_n = n^2 - 2n + 3

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Solution

We will substitute the values of nn from 1 to 5 into each given formula.

Step 1 — Find terms for tn=3n4t_n = 3n - 4

Let's find the first term by setting n=1n = 1.

t1=3(1)4t_1 = 3(1) - 4

=34= 3 - 4

1\boxed{-1}

Let's find the second term by setting n=2n = 2.

t2=3(2)4t_2 = 3(2) - 4

=64= 6 - 4

2\boxed{2}

Let's find the third term by setting n=3n = 3.

t3=3(3)4t_3 = 3(3) - 4

=94= 9 - 4

5\boxed{5}

Let's find the fourth term by setting n=4n = 4.

t4=3(4)4t_4 = 3(4) - 4

=124= 12 - 4

8\boxed{8}

Let's find the fifth term by setting n=5n = 5.

t5=3(5)4t_5 = 3(5) - 4

=154= 15 - 4

11\boxed{11}

Step 2 — Find terms for tn=25nt_n = 2 - 5n

Let's find the first term by setting n=1n = 1.

t1=25(1)t_1 = 2 - 5(1)

=25= 2 - 5

3\boxed{-3}

Let's find the second term by setting n=2n = 2.

t2=25(2)t_2 = 2 - 5(2)

=210= 2 - 10

8\boxed{-8}

Let's find the third term by setting n=3n = 3.

t3=25(3)t_3 = 2 - 5(3)

=215= 2 - 15

13\boxed{-13}

Let's find the fourth term by setting n=4n = 4.

t4=25(4)t_4 = 2 - 5(4)

=220= 2 - 20

18\boxed{-18}

Let's find the fifth term by setting n=5n = 5.

t5=25(5)t_5 = 2 - 5(5)

=225= 2 - 25

23\boxed{-23}

Step 3 — Find terms for tn=n22n+3t_n = n^2 - 2n + 3

Let's find the first term by setting n=1n = 1.

t1=122(1)+3t_1 = 1^2 - 2(1) + 3

=12+3= 1 - 2 + 3

2\boxed{2}

Let's find the second term by setting n=2n = 2.

t2=222(2)+3t_2 = 2^2 - 2(2) + 3

=44+3= 4 - 4 + 3

3\boxed{3}

Let's find the third term by setting n=3n = 3.

t3=322(3)+3t_3 = 3^2 - 2(3) + 3

=96+3= 9 - 6 + 3

6\boxed{6}

Let's find the fourth term by setting n=4n = 4.

t4=422(4)+3t_4 = 4^2 - 2(4) + 3

=168+3= 16 - 8 + 3

11\boxed{11}

Let's find the fifth term by setting n=5n = 5.

t5=522(5)+3t_5 = 5^2 - 2(5) + 3

=2510+3= 25 - 10 + 3

18\boxed{18}

Answer

(i) The first five terms are -1, 2, 5, 8, 11. (ii) The first five terms are -3, -8, -13, -18, -23. (iii) The first five terms are 2, 3, 6, 11, 18.

More questions in Exercise 8.1

Q1

Find the first five terms of the sequence in which the nthn^{\text{th}} term is given by, for n1n \ge 1:

(i) tn=3n4t_n = 3n - 4

(ii) tn=25nt_n = 2 - 5n

(iii) tn=n22n+3t_n = n^2 - 2n + 3

Q2

Find the 10th10^{\text{th}} and 15th15^{\text{th}} terms of the sequence tn=5n3t_n = 5n - 3 for n1n \ge 1.

Q3

Determine whether 97 and 172 are terms of the sequence tn=5n3t_n = 5n - 3 for n1n \ge 1.

Q4

Which term of the sequence tn=5n3t_n = 5n - 3 for n1n \ge 1 is 607?

Q5

A sequence is given by the recursive rule t1=5t_1 = -5, tn+1=tn+3t_{n+1} = t_n + 3 for n1n \ge 1. Find the first five terms of the sequence. Is 52 a term of this sequence? If so, which term is it?

Q6

Let T1=1T_1 = 1, T2=2T_2 = 2, T3=4T_3 = 4, and Tn=Tn1+Tn2+Tn3T_n = T_{n-1} + T_{n-2} + T_{n-3} for n4n \ge 4. Find T4,T5,T6,T7,T_4, T_5, T_6, T_7, and T8T_8.

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