## EXERCISE 1.5

#### Page No 24:

#### Question 1:

Classify the following numbers as rational or irrational:

(i) (ii) (iii)

(iv) (v) 2π

#### Answer:

(i) = 2 − 2.2360679…

= − 0.2360679…

As the decimal expansion of this expression is non-terminating non-recurring, therefore, it is an irrational number.

(ii)

As it can be represented in form, therefore, it is a rational number.

(iii)

As it can be represented in form, therefore, it is a rational number.

(iv)

As the decimal expansion of this expression is non-terminating non-recurring, therefore, it is an irrational number.

(v) 2π = 2(3.1415 …)

= 6.2830 …

As the decimal expansion of this expression is non-terminating non-recurring, therefore, it is an irrational number.

#### Question 2:

Simplify each of the following expressions:

(i) (ii)

(iii) (iv)

#### Answer:

(i)

(ii)

= 9 − 3 = 6

(iii)

(iv)

= 5 − 2 = 3

#### Question 3:

Recall, π is defined as the ratio of the circumference (say *c*) of a circle to its diameter (say *d*). That is, . This seems to contradict the fact that π is irrational. How will you resolve this contradiction?

#### Answer:

There is no contradiction. When we measure a length with scale or any other instrument, we only obtain an approximate rational value. We never obtain an exact value. For this reason, we may not realise that either *c* or *d* is irrational. Therefore, the fraction is irrational. Hence, π is irrational.

#### Question 4:

Represent on the number line.

#### Answer:

Mark a line segment OB = 9.3 on number line. Further, take BC of 1 unit. Find the mid-point D of OC and draw a semi-circle on OC while taking D as its centre. Draw a perpendicular to line OC passing through point B. Let it intersect the semi-circle at E. Taking B as centre and BE as radius, draw an arc intersecting number line at F. BF is.

#### Question 5:

Rationalise the denominators of the following:

(i) (ii)

(iii) (iv)

#### Answer:

(i)

(ii)

(iii)

(iv)