Will you square ??? Part:2

Algebra Level 3

If 18 + 308 + 15 + 104 = e a + f b + g c + h d \sqrt { 18+\sqrt { 308 } } +\sqrt { 15+\sqrt { 104 } } =e\sqrt { a } +f\sqrt { b } +g\sqrt { c } +h\sqrt { d } \\ ,where a , b , c , d , e , f , g , h a,b,c,d,e,f,g,h are positive integers.Then find the value of a + b + c + d a+b+c+d .


The answer is 33.

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2 solutions

Shivamani Patil
Sep 4, 2014

First we have

18 + 308 = 18 + 2 77 = 11 + 7 + 2 11 × 7 = ( 11 + 7 ) 2 = 11 + 7 \sqrt { 18+\sqrt { 308 } } =\sqrt { 18+2\sqrt { 77 } } =\sqrt { 11+7+2\sqrt { 11 } \times \sqrt { 7 } } =\sqrt { { \left( \sqrt { 11 } +\sqrt { 7 } \right) }^{ 2 } } =\sqrt { 11 } +\sqrt { 7 }

Similarly

15 + 104 = 15 + 2 26 = 13 + 2 + 2 13 × 2 = ( 13 + 2 ) 2 = 13 + 2 \sqrt { 15+\sqrt { 104 } } =\sqrt { 15+2\sqrt { 26 } } =\sqrt { 13+2+2\sqrt { 13 } \times \sqrt { 2 } } =\sqrt { { \left( \sqrt { 13 } +\sqrt { 2 } \right) }^{ 2 } } =\sqrt { 13 } +\sqrt { 2 }

Therefore

e a + f b + g c + h d = 11 + 7 + 13 + 2 e\sqrt { a } +f\sqrt { b } +g\sqrt { c } +h\sqrt { d } =\sqrt { 11 } +\sqrt { 7 } +\sqrt { 13 } +\sqrt { 2 }

Therefore a + b + c + d = 13 + 2 + 11 + 7 = 33 a+b+c+d=13+2+11+7=33

Nice solution @shivamani patil . Can you prove that no other solutions exist? Thanks.

Satvik Golechha - 6 years, 8 months ago

0verrated .......................................

math man - 6 years, 8 months ago

There is some correction in the solution. You missed the letter e e in the statement:

e a + f b + g c + h d = 11 + 7 + 13 + 2 e\sqrt{a}+f\sqrt{b}+g\sqrt{c}+h\sqrt{d}=\sqrt{11}+\sqrt{7}+\sqrt{13}+\sqrt{2}

Saurabh Mallik - 6 years, 8 months ago

good solution. I used reverse engineering from a past problem's solution.

Anurag Pandey - 5 years, 3 months ago

Bro I can't believe youre 14. This is too clever. Cool!

Ceesay Muhammed - 6 years, 7 months ago
Saurabh Mallik
Sep 23, 2014

First, we need to remove the square root sign to make it simpler to solve.

18 + 308 \sqrt{18+\sqrt{308}}

= 18 + 2 77 =\sqrt{18+2\sqrt{77}}

= 11 + 7 + 2 77 =\sqrt{11+7+2\sqrt{77}}

= ( 11 ) 2 + ( 7 ) 2 + 2 × 11 × 7 =\sqrt{(\sqrt{11})^{2}+(\sqrt{7})^{2}+2\times\sqrt{11}\times\sqrt{7}}

= ( 11 + 7 ) 2 = 11 + 7 =\sqrt{(\sqrt{11}+\sqrt{7})^{2}}=\sqrt{11}+\sqrt{7}

Similarly, we will solve for the second one.

15 + 104 \sqrt{15+\sqrt{104}}

= 15 + 2 26 =\sqrt{15+2\sqrt{26}}

= 13 + 2 + 2 26 =\sqrt{13+2+2\sqrt{26}}

= ( 13 ) 2 + ( 2 ) 2 + 2 × 13 × 2 =\sqrt{(\sqrt{13})^{2}+(\sqrt{2})^{2}+2\times\sqrt{13}\times\sqrt{2}}

= ( 13 + 2 ) 2 = 13 + 2 =\sqrt{(\sqrt{13}+\sqrt{2})^{2}}=\sqrt{13}+\sqrt{2}

So, 18 + 308 + 15 + 104 = 11 + 7 + 13 + 2 \sqrt{18+\sqrt{308}}+\sqrt{15+\sqrt{104}}=\sqrt{11}+\sqrt{7}+\sqrt{13}+\sqrt{2}

Therefore,

e a + f b + g c + h d = 11 + 7 + 13 + 2 e\sqrt{a}+f\sqrt{b}+g\sqrt{c}+h\sqrt{d}=\sqrt{11}+\sqrt{7}+\sqrt{13}+\sqrt{2}

Therefore, the answer is: a + b + c + d = 11 + 7 + 13 + 2 = 33 a+b+c+d=11+7+13+2=\boxed{33}

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