1.

Write ‘T’ for true and ‘F’ for false for each of the following: (i) Rational numbers are always closed under subtraction. (ii) Rational numbers are always closed under division.(iii) \(1\div0=0.\)(iv) Subtraction is commutative on rational numbers.(v) \(-(\frac{-7}{8})=\frac{7}{8}.\)

Answer»

(i) true 

Let there be two rational numbers \(\frac{a}{b}\) and \(\frac{c}{d}\)

Then,

\(\frac{a}{b}-\frac{c}{d}= \frac{ad-bc}{bd}\) 

which is also a rational number

Hence, 

Rational numbers are always closed under subtraction.

(ii) false

\(\frac{a}{0}=\infty\)

Hence, 

Rational numbers are not always closed under division.

(iii) false

\(\frac{1}{0}=\infty\)

Hence, \(\frac{1}{0}=\infty\) 

(iv) false

Let there be two rational numbers \(\frac{a}{b}\) and \(\frac{c}{d}\) 

Then,

\(\frac{a}{b}-\frac{c}{d}=\frac{ad-bc}{bd}\)

And

\(\frac{c}{d}-\frac{a}{b}=\frac{bc-ad}{bd}\)

Therefore,

\(\frac{a}{b}-\frac{c}{d}\neq\frac{c}{d}-\frac{a}{b}\)

Hence, 

Subtraction is not commutative on rational numbers.

(v) true

\((\frac{-7}{8})=-1\times\frac{-7}{8}=\frac{7}{8}\)



Discussion

No Comment Found

Related InterviewSolutions