Welcome 2016! Part 10

Algebra Level 2

2 × 3 3 × 4 4 = b a \large \sqrt{2} \times \sqrt[3]{3} \times \sqrt[4]{4} = \sqrt[a]{b}

If a a and b b are positive integers, find the least value of a + b a+b .


The answer is 27.

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3 solutions

Akhil Bansal
Dec 14, 2015

= 2 1 2 × 3 1 3 × 4 1 4 \large= 2^{\frac{1}{2}} \times 3^{\frac{1}{3}} \times 4^{\frac{1}{4}} = 2 1 2 × 3 1 3 × 2 2 4 \large= 2^{\frac{1}{2}} \times 3^{\frac{1}{3}} \times 2^{\frac{2}{4}} = 2 × 3 1 3 \large= 2 \times 3^{\frac{1}{3}} = 8 1 3 × 3 1 3 \large = 8^{\frac{1}{3}} \times 3^{\frac{1}{3}} = 2 4 1 3 \large = 24^{\frac{1}{3}}

ans will be 27...am I right???

Md. Rakibul Hasan Rakib - 5 years, 6 months ago

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Yes. 576 6 , 13824 9 , 331776 12 , 7962624 15 \displaystyle \sqrt[6]{576}, \displaystyle \sqrt[9]{13824}, \displaystyle \sqrt[12]{331776}, \displaystyle \sqrt[15]{7962624} and etc can be the possibilities otherwise.

Lu Chee Ket - 5 years, 6 months ago

2 × 3 3 × 4 4 = 2 1 2 × 3 1 3 × 4 1 4 = 2 1 2 × 3 1 3 × ( 2 2 ) 1 4 = 2 1 2 × 3 1 3 × 2 1 2 = 2 × 3 1 3 = 2 3 3 = 3 ( 8 ) 3 = 24 3 \sqrt{2}\times\sqrt[3]{3}\times\sqrt[4]{4}\\={2}^{\frac{1}{2}}\times{3}^{\frac{1}{3}}\times{4}^{\frac{1}{4}}\\={2}^{\frac{1}{2}}\times{3}^{\frac{1}{3}}\times{({2}^{2})}^{\frac{1}{4}}\\={2}^{\frac{1}{2}}\times{3}^{\frac{1}{3}}\times{2}^{\frac{1}{2}}\\={2}\times{3}^{\frac{1}{3}}\\=2\sqrt[3]{3}\\=\sqrt[3]{3(8)}\\=\sqrt[3]{24}

Substituting b a \sqrt[a]{b} with the values of the solution, we get that 3 + 24 = 27 3+24=\boxed{27} .

Sonveer Yadav
Dec 18, 2015

2 1 / 2 2^{1/2} × 3 1 / 3 3^{1/3} × 4 1 / 4 4^{1/4} = b 1 / a b^{1/a} .
2 1 / 2 2^{1/2} × 3 1 / 3 3^{1/3} × 2 1 / 2 2^{1/2} = b 1 / a b^{1/a}

2 × 3 1 / 3 3^{1/3} = b 1 / a b^{1/a}

8 1 / 3 8^{1/3} × 3 1 / 3 3^{1/3} = b 1 / a b^{1/a}

2 4 1 / 3 24^{1/3} = b 1 / a b^{1/a}

a+b= 3+24=27

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