{"id":10429,"date":"2022-04-09T20:39:57","date_gmt":"2022-04-09T15:09:57","guid":{"rendered":"https:\/\/mathemerize.com\/?p=10429"},"modified":"2022-04-09T22:32:22","modified_gmt":"2022-04-09T17:02:22","slug":"prove-that-the-following-are-irrationals","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/prove-that-the-following-are-irrationals\/","title":{"rendered":"Prove that the following are irrationals :"},"content":{"rendered":"
Question<\/strong> : Prove that the following are irrationals :<\/p>\n (i) \\(1\\over \\sqrt{2}\\)<\/p>\n (ii) \\(7\\sqrt{5}\\)<\/p>\n (iii) \\(6 + \\sqrt{2}\\)<\/p>\n Solution<\/strong> :<\/p>\n (i) <\/strong> Let us assume, to the contrary, that \\(1\\over \\sqrt{2}\\) is rational. That is, we can find co-prime integers p and q (q \\(\\ne\\) 0) such that<\/p>\n \\(1\\over \\sqrt{2}\\) = \\(p\\over q\\) or \\(1\\times \\sqrt{2}\\over \\sqrt{2}\\times \\sqrt{2}\\) = \\(p\\over q\\) or \\(\\sqrt{2}\\over 2\\) = \\(p\\over q\\)<\/p>\n or \\(\\sqrt{2}\\) = \\(2p\\over q\\)<\/p>\n Since p and q are integers \\(2p\\over q\\) is rational, and so \\(\\sqrt{2}\\) is rational.<\/p>\n But this contradicts the fact that \\(\\sqrt{2}\\) is irrational.<\/p>\n so, we conclude that \\(1\\over \\sqrt{2}\\) is an irrational.<\/strong><\/p>\n (ii)<\/strong> Let us assume, to the contrary, that \\(7\\sqrt{5}\\) is rational. That is, we can find co-prime integers p and q (q \\(\\ne\\) 0) such that \\(7\\sqrt{5}\\) = \\(p\\over q\\).<\/p>\n So, \\(\\sqrt{5}\\) = \\(p\\over 7q\\)<\/p>\n Since p and q are integers, \\(p\\over 7q\\) is rational and so is \\(\\sqrt{5}\\).<\/p>\n But this contradicts the fact that \\(\\sqrt{5}\\) is irrational. So, we conclude that \\(7\\sqrt{5}\\) is an irrational.<\/strong><\/p>\n (iii)<\/strong> Let us assume, to the contrary, that \\(6 + \\sqrt{2}\\) is rational. That is, we can find co-prime integers p and q (q \\(\\ne\\) 0) such that<\/p>\n \\(6 + \\sqrt{2}\\) = \\(p\\over q\\) or 6 – \\(p\\over q\\) = \\(\\sqrt{2}\\)<\/p>\n or \\(\\sqrt{2}\\) = 6 – \\(p\\over q\\)<\/p>\n Since p and q are integers, 6 – \\(p\\over q\\) is rational, and so \\(\\sqrt{2}\\) is rational.<\/p>\n But this contradicts the fact that \\(\\sqrt{2}\\) is irrational.<\/p>\n so, we conclude that \\(6 + \\sqrt{2}\\) is an irrational.<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":" Question : Prove that the following are irrationals : (i) \\(1\\over \\sqrt{2}\\) (ii) \\(7\\sqrt{5}\\) (iii) \\(6 + \\sqrt{2}\\) Solution : (i) Let us assume, to the contrary, that \\(1\\over \\sqrt{2}\\) is rational. That is, we can find co-prime integers p and q (q \\(\\ne\\) 0) such that \\(1\\over \\sqrt{2}\\) = \\(p\\over q\\) or \\(1\\times \\sqrt{2}\\over …<\/p>\n