

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