Arithmetic Progressions | Exercise 5.1

Question 2

  1. Write first four terms of the AP, when the first term aa and the common difference dd are given as follows:

(i) a=10,d=10a = 10, \quad d = 10

(ii) a=2,d=0a = -2, \quad d = 0

(iii) a=4,d=3a = 4, \quad d = -3

(iv) a=1,d=12a = -1, \quad d = \frac{1}{2}

(v) a=1.25,d=0.25a = -1.25, \quad d = -0.25

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Solution

We find each term by adding the common difference to the previous term.

Step 1 — Calculate terms for (i)

Here, the first term aa is 10. The common difference dd is 10. Let's find the first term a1a_1. a1=aa_1 = a a1=10a_1 = 10 Let's find the second term a2a_2. a2=a1+da_2 = a_1 + d a2=10+10a_2 = 10 + 10 =20= 20 Let's find the third term a3a_3. a3=a2+da_3 = a_2 + d a3=20+10a_3 = 20 + 10 =30= 30 Let's find the fourth term a4a_4. a4=a3+da_4 = a_3 + d a4=30+10a_4 = 30 + 10 =40= 40 The first four terms are:

10,20,30,40\boxed{10, 20, 30, 40}

Diagram 1

Step 2 — Calculate terms for (ii)

Here, the first term aa is -2. The common difference dd is 0. Let's find the first term a1a_1. a1=aa_1 = a a1=2a_1 = -2 Let's find the second term a2a_2. a2=a1+da_2 = a_1 + d a2=2+0a_2 = -2 + 0 =2= -2 Let's find the third term a3a_3. a3=a2+da_3 = a_2 + d a3=2+0a_3 = -2 + 0 =2= -2 Let's find the fourth term a4a_4. a4=a3+da_4 = a_3 + d a4=2+0a_4 = -2 + 0 =2= -2 The first four terms are:

2,2,2,2\boxed{-2, -2, -2, -2}

Step 3 — Calculate terms for (iii)

Here, the first term aa is 4. The common difference dd is -3. Let's find the first term a1a_1. a1=aa_1 = a a1=4a_1 = 4 Let's find the second term a2a_2. a2=a1+da_2 = a_1 + d a2=4+(3)a_2 = 4 + (-3) =1= 1 Let's find the third term a3a_3. a3=a2+da_3 = a_2 + d a3=1+(3)a_3 = 1 + (-3) =2= -2 Let's find the fourth term a4a_4. a4=a3+da_4 = a_3 + d a4=2+(3)a_4 = -2 + (-3) =5= -5 The first four terms are:

4,1,2,5\boxed{4, 1, -2, -5}

Step 4 — Calculate terms for (iv)

Here, the first term aa is -1. The common difference dd is 12\frac{1}{2}. Let's find the first term a1a_1. a1=aa_1 = a a1=1a_1 = -1 Let's find the second term a2a_2. a2=a1+da_2 = a_1 + d a2=1+12a_2 = -1 + \frac{1}{2} =12= -\frac{1}{2} Let's find the third term a3a_3. a3=a2+da_3 = a_2 + d a3=12+12a_3 = -\frac{1}{2} + \frac{1}{2} =0= 0 Let's find the fourth term a4a_4. a4=a3+da_4 = a_3 + d a4=0+12a_4 = 0 + \frac{1}{2} =12= \frac{1}{2} The first four terms are:

1,12,0,12\boxed{-1, -\frac{1}{2}, 0, \frac{1}{2}}

Step 5 — Calculate terms for (v)

Here, the first term aa is -1.25. The common difference dd is -0.25. Let's find the first term a1a_1. a1=aa_1 = a a1=1.25a_1 = -1.25 Let's find the second term a2a_2. a2=a1+da_2 = a_1 + d a2=1.25+(0.25)a_2 = -1.25 + (-0.25) =1.50= -1.50 Let's find the third term a3a_3. a3=a2+da_3 = a_2 + d a3=1.50+(0.25)a_3 = -1.50 + (-0.25) =1.75= -1.75 Let's find the fourth term a4a_4. a4=a3+da_4 = a_3 + d a4=1.75+(0.25)a_4 = -1.75 + (-0.25) =2.00= -2.00 The first four terms are:

1.25,1.50,1.75,2.00\boxed{-1.25, -1.50, -1.75, -2.00}

Answer

(i) The first four terms are 10,20,30,4010, 20, 30, 40. (ii) The first four terms are 2,2,2,2-2, -2, -2, -2. (iii) The first four terms are 4,1,2,54, 1, -2, -5. (iv) The first four terms are 1,12,0,12-1, -\frac{1}{2}, 0, \frac{1}{2}. (v) The first four terms are 1.25,1.50,1.75,2.00-1.25, -1.50, -1.75, -2.00.

More questions in Exercise 5.1

Q1

In which of the following situations, does the list of numbers involved make an arithmetic progression, and why?

(i) The taxi fare after each km when the fare is ₹ 15 for the first km and ₹ 8 for each additional km.

(ii) The amount of air present in a cylinder when a vacuum pump removes 14\frac{1}{4} of the air remaining in the cylinder at a time.

(iii) The cost of digging a well after every metre of digging, when it costs ₹ 150 for the first metre and rises by ₹ 50 for each subsequent metre.

(iv) The amount of money in the account every year, when ₹ 10000 is deposited at compound interest at 8 % per annum.

Q2
  1. Write first four terms of the AP, when the first term aa and the common difference dd are given as follows:

(i) a=10,d=10a = 10, \quad d = 10

(ii) a=2,d=0a = -2, \quad d = 0

(iii) a=4,d=3a = 4, \quad d = -3

(iv) a=1,d=12a = -1, \quad d = \frac{1}{2}

(v) a=1.25,d=0.25a = -1.25, \quad d = -0.25

Q3
  1. For the following APs, write the first term and the common difference:

(i) 3,1,1,3,3, 1, -1, -3, \dots

(ii) 5,1,3,7,-5, -1, 3, 7, \dots

(iii) 13,53,93,133,\frac{1}{3}, \frac{5}{3}, \frac{9}{3}, \frac{13}{3}, \dots

(iv) 0.6,1.7,2.8,3.9,0.6, 1.7, 2.8, 3.9, \dots

Q4
  1. Which of the following are APs ? If they form an AP, find the common difference dd and write three more terms.

(i) 2,4,8,16,2, 4, 8, 16, \dots

(ii) 2,52,3,72,2, \frac{5}{2}, 3, \frac{7}{2}, \dots

(iii) 1.2,3.2,5.2,7.2,-1.2, -3.2, -5.2, -7.2, \dots

(iv) 10,6,2,2,-10, -6, -2, 2, \dots

(v) 3,3+2,3+22,3+32,3, 3 + \sqrt{2}, 3 + 2\sqrt{2}, 3 + 3\sqrt{2}, \dots

(vi) 0.2,0.22,0.222,0.2222,0.2, 0.22, 0.222, 0.2222, \dots

(vii) 0,4,8,12,0, -4, -8, -12, \dots

(viii) 12,12,12,12,-\frac{1}{2}, -\frac{1}{2}, -\frac{1}{2}, -\frac{1}{2}, \dots

(ix) 1,3,9,27,1, 3, 9, 27, \dots

(x) a,2a,3a,4a,a, 2a, 3a, 4a, \dots

(xi) a,a2,a3,a4,a, a^2, a^3, a^4, \dots

(xii) 2,8,18,32,\sqrt{2}, \sqrt{8}, \sqrt{18}, \sqrt{32}, \dots

(xiii) 3,6,9,12,\sqrt{3}, \sqrt{6}, \sqrt{9}, \sqrt{12}, \dots

(xiv) 12,32,52,72,1^2, 3^2, 5^2, 7^2, \dots

(xv) 12,52,72,73,1^2, 5^2, 7^2, 73, \dots

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