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Real Numbers

Question
CBSEENMA10006141

The following real numbers have decimal expansions as given below. In each case, decide whether they are rational or not. If they are rational, and of the form , p q what can you say about the prime factors of q?

(i) 43.123456789

Solution
left parenthesis straight i right parenthesis space 43.123456789 space space equals 43123456789 over 1000000000
space space space space space space space space space space space space space space space space space space space space space space space space space space equals 43123456789 over 10 to the power of 9
space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator 43123456789 over denominator 2 to the power of 9 cross times 5 to the power of 9 end fraction

∴ 43.123456789 is a rational number of the form p/q, where ‘p’ and ‘q’ are co-primes and the prime factors of ‘q’ are of the form 2n.5n, where n is nonnegative integer.