Q9 of 21 Page 14

Determine whether the argument used to check the validity of the following statement is correct:

p: “If x2 is irrational, then x is rational.”


The statement is true because the number x2 = π2 is irrational, therefore x = π is irrational.

Argument Used: x2 = π2 is irrational, therefore x = π is irrational.


p: “If x2 is irrational, then x is rational.”


Let us take an irrational number given by x = √k, where k is a rational number.


Squaring both sides, we get,


x2 = k


Therefore, x2 is a rational number and contradicts our statement.


Hence, the given argument is wrong.

More from this chapter

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4

Determine whether in the given statements an inclusive “OR” or exclusive “OR” is used.

(i) Sun rises or moon sets


(ii) Two lines intersect at a point or are parallel.


(iii) The school is closed if it is holiday or a Sunday.

8

Identify the quantifier in the following statements and write the negation of the statements.

(i) There exists a number which is equal to its square.


(ii) For every real number x, x is less than x + 1.


(iii) There exists a capital for every state in India.

10

Rewrite each of the following statements in the form “p if and only is q.”

(i) p : If you watch television, then your mind is free, and if your mind is free, then you watch television.


(ii) q : If a quadrilateral is equiangular, then it is a rectangle, and if a quadrilateral is a rectangle, then it is equiangular.


(iii) r : For you to get an A grade, it is necessary and sufficient that you do all the homework you regularly.


(iv) s : If a tumbler is half empty, then it is half full, and if a tumbler is half full, then it is half empty.

11

Write the component statements of the following compound statements and check whether the compound statement is true or false:

(i) To enter into a public library children need an identification card from the school or a letter from the school authorities.


(ii) All rational numbers are real and all real numbers are not complex.


(iii) Square of an integer is positive or negative.


(iv) x = 2 and x = 3 are the roots of the equation 3x2 – x – 10 = 0.


(v) The sand heats up quickly in the sun and does not cool down fast at night.