An algebra problem by shiv kumar

Algebra Level 2

If 5 + 2 6 \sqrt{5+2\sqrt{6}} can be expressed in the form a + b \sqrt a+\sqrt b where a a and b b are positive integers, then find the value of a + b a+b .


The answer is 5.

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3 solutions

Trevor Arashiro
Sep 17, 2014

First, we take away the radical and we have 5 + 2 6 5+2\sqrt6 . Now, for this to be represented in a + b \sqrt a+\sqrt b , we need to find ( a + b ) 2 = a + b + 2 a b (\sqrt a+\sqrt b)^2=a+b+2\sqrt{ab} . Since a,b are integers, a must be equal to 1 or 2 while b is equal to either 4 or 3. Checking 2 and 3: ( 2 + 3 ) 2 = 2 + 2 6 + 3 5 + 2 6 (\sqrt2+\sqrt3)^2=2+2\sqrt6+3\Rightarrow 5+2\sqrt6

nice but try giving more solutions

shiv kumar - 6 years, 8 months ago

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Sorry, posted my first solution in quite a rush.

Trevor Arashiro - 6 years, 8 months ago

Brilliant Answer!!

shiv kumar - 6 years, 8 months ago

it is ok man chill!!

shiv kumar - 6 years, 8 months ago

You can refer my solution. I have posted with much precision.

Saurabh Mallik - 6 years, 8 months ago
Saurabh Mallik
Sep 23, 2014

We can write this in the following way as well.

5 + 2 6 \sqrt{5+2\sqrt{6}}

= 2 + 3 + 2 6 =\sqrt{2+3+2\sqrt{6}}

= ( 2 ) 2 + ( 3 ) 2 + 2 × 2 × 3 =\sqrt{(\sqrt{2})^{2}+(\sqrt{3})^{2}+2\times\sqrt{2}\times\sqrt{3}}

= ( 2 + 3 ) 2 = 2 + 3 =\sqrt{(\sqrt{2}+\sqrt{3})^{2}}=\sqrt{2}+\sqrt{3}

5 + 2 6 = 2 + 3 = a + b \sqrt{5+2\sqrt{6}}=\sqrt{2}+\sqrt{3}=\sqrt{a}+\sqrt{b}

Therefore, the answer is: a + b = 2 + 3 = 5 a+b=2+3=\boxed{5}

Rohit Sachdeva
Oct 9, 2014

x = 5 + 2 6 x=5+2\sqrt{6}

x = a + b \sqrt{x}=\sqrt{a}+\sqrt{b}

x = a + b + 2 a b x=a+b+2\sqrt{ab}

5 + 2 6 = ( a + b ) + 2 a b 5+2\sqrt{6}=(a+b)+2\sqrt{ab}

Comparing both sides, a+b=5

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