Just 1+1

Algebra Level 2

Let x = 1 + 1 x=1+1 . If x x can be expressed in the form m n \frac{m}{n} , where m m and n n are coprime, positive integers, and 2 ( m 2 + n 2 + 2 m n ) = 2 a × 3 b 2(m^{2}+n^{2}+2mn)=2^{a} \times 3^{b} , what is the value of a + b a+b ?


The answer is 3.

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4 solutions

Ashish Menon
May 28, 2016

1 + 1 = 2 1 1 + 1 =\dfrac{2}{1} . So, m = 2 m = 2 and n = 1 n = 1 . Now, 2 ( m 2 + n 2 + 2 m n ) = 2 ( m + n ) 2 = 2 × 3 2 2(m^2 + n^2 + 2mn) =2{(m + n)}^2 = 2×3^2 . So, a + b = 3 a + b = \color{#69047E}{\boxed{3}} .

Hello,

as x= 1+1 =2, it also can be written as m/n= 2 / 2^0,

m = 2 , n= 2^0 = 1,substitute them into the equation,

2(4 + 1 + 2(2)(1) )= 2^a . 3^b,

2^a . 3^b = 18=2 x 9

2^a . 3^b = 2 x 3^2

a=1, b=2, therefore, a+b = 1+2 = 3...

thanks....

Nikko Quirap
Apr 11, 2014

2=2/1 2=m/n 2(m^ 2 + n^2 + 2mn) = 2^a * 3^b m=b n=a 18=2^n * 3^m m+n=a+b a+b=3

Shabarish Ch
Mar 3, 2014

x = 1 + 1 = 2 x = 1 + 1 = 2

The only way to express 2 as m n \frac{m}{n} where m m and n n are co-prime positive integers is 2 1 \frac{2}{1} . This implies that m = 2 m = 2 and n = 1 n = 1 .

Substituting the values of m m and n n in the expression 2 ( m 2 + n 2 + 2 m n ) 2( m^2 + n^2 + 2mn) , we get 18.

Now, 18 = 2 1 × 3 2 18 = 2^1 \times 3^2 , which implies that a = 1 a = 1 and b = 2 b = 2 .

So, a + b = 1 + 2 = 3 a + b = 1 + 2 = \boxed{3}

Aaaaahhhhhh. I new that m=2 and N=1, but I didn't see the multiplication sign for the last part so I thought I did something wrong

Robert Fritz - 7 years, 3 months ago

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