Advertisements
Advertisements
Question
Show that the statement
p: “If x is a real number such that x3 + 4x = 0, then x is 0” is true by
(i) direct method
(ii) method of contradiction
(iii) method of contrapositive
Advertisements
Solution
p: “If x is a real number such that x3 + 4x = 0, then x is 0”.
Let q: x is a real number such that x3 + 4x = 0
r: x is 0.
(i) To show that statement p is true, we assume that q is true and then show that r is true.
Therefore, let statement q be true.
∴ x3 + 4x = 0
x (x2 + 4) = 0
⇒ x = 0 or x2 + 4 = 0
However, since x is real, it is 0.
Thus, statement r is true.
Therefore, the given statement is true.
(ii) To show statement p to be true by contradiction, we assume that p is not true.
Let x be a real number such that x3 + 4x = 0 and let x is not 0.
Therefore, x3 + 4x = 0
x (x2 + 4) = 0
x = 0 or x2 + 4 = 0
x = 0 or x2 = – 4
However, x is real. Therefore, x = 0, which is a contradiction since we have assumed that x is not 0.
Thus, the given statement p is true.
(iii) To prove statement p to be true by contrapositive method, we assume that r is false and prove that qmust be false.
Here, r is false implies that it is required to consider the negation of statement r. This obtains the following statement.
∼r: x is not 0.
It can be seen that (x2 + 4) will always be positive.
x ≠ 0 implies that the product of any positive real number with x is not zero.
Let us consider the product of x with (x2 + 4).
∴ x (x2 + 4) ≠ 0
⇒ x3 + 4x ≠ 0
This shows that statement q is not true.
Thus, it has been proved that
∼r ⇒ ∼q
Therefore, the given statement p is true
APPEARS IN
RELATED QUESTIONS
By giving a counter example, show that the following statements are not true.
p: If all the angles of a triangle are equal, then the triangle is an obtuse angled triangle.
Find out the sentence are statement and are not. Justify your answer.
Every set is a finite set.
Find out the sentence are statement and are not. Justify your answer.
The cat pussy is black.
Find out the sentence are statement and are not. Justify your answer.
The product of (−1) and 8 is 8.
All birds sing.
There is a complex number which is not a real number.
I will not go to school.
Write the negation of the statement:
r : There exists a number x such that 0 < x < 1.
Write the component statement of the compound statement and check whether the compound statement is true or false:
Square of an integer is positive or negative.i
Write the component statement of the compound statement and check whether the compound statement is true or false:
x = 2 and x = 3 are the roots or the equation 3x2 − x − 10 = 0.
Write the component statement of the compound statement and check whether the compound statement is true or false:
The sand heats up quickly in the sun and does not cool down fast at night.
Determine whether the compound statement are true or false:
Delhi is in England and 2 + 2 = 4.
Determine whether the compound statement are true or false:
Delhi is in England and 2 + 2 =5.
Write the negation of statement:
For every x ϵ N, x + 3 < 10
Negate of the statement :
There exists a number which is equal to its square.
statement are true and false? In each case give a valid reason for saying so
p : Each radius of a circle is a chord of the circle.
statement are true and false? In each case give a valid reason for saying so
r : Circle is a particular case of an ellipse.
Identify the component statements and the connective in the following compound statements.
It is raining or the sun is shining.
Translate the following statements in symbolic form
2 and 3 are prime numbers
Express in English, the statement p → q, where
p: It is raining today
q: 2 + 3 > 4
Translate the following biconditional into symbolic form:
“ABC is an equilateral triangle if and only if its each interior angle is 60°”
Which of the following sentences are statements? Justify
y + 9 = 7.
Find the component statements of the following compound statements.
Chennai is in India and is the capital of Tamil Nadu.
Find the component statements of the following compound statements.
`sqrt(7)` is a rational number or an irrational number.
Find the component statements of the following compound statements.
A rectangle is a quadrilateral or a 5-sided polygon.
Write the component statements of the following compound statements and check whether the compound statement is true or false.
24 is a multiple of 4 and 6.
Write down the negation of following compound statements
All rational numbers are real and complex.
Write down the negation of following compound statements
6 is divisible by 2 and 3.
Form the biconditional statement p ↔ q, where
p: A natural number n is odd.
q: Natural number n is not divisible by 2.
Identify the Quantifiers in the following statements.
There exists a triangle which is not equilateral.
Identify the Quantifiers in the following statements.
For every natural number x, x + 1 is also a natural number.
Identify the Quantifiers in the following statements.
For all negative integers x, x 3 is also a negative integers.
Identify the Quantifiers in the following statements.
There exists a statement in above statements which is not true.
Check the validity of the following statement.
q: 131 is a multiple of 3 or 11
The connective in the statement “Earth revolves round the Sun and Moon is a satellite of earth” is ______.
Which of the following statement is a conjunction?
