Mathematical mistakes are interesting

Algebra Level 3

Professor Ávila gave Esmeralda an equation of the form a x = b ax = b , where a a and b b are real numbers. Esmeralda, by accident, solved the equation b x = a bx = a and got a solution that is equal to the correct one minus 60. If the correct solution is of the form m + n m + \sqrt{n} , where m m and n n are integers, what is the value of m + n m + n ?


Source: Brazilian Maths Olympiad (OBM), 2015.


The answer is 931.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

a x = b x = b a = R ax = b \Rightarrow x = \frac{b}{a} = R ; b x = a x = a b = r bx = a \Rightarrow x = \frac{a}{b} = r ; a b = 1 b a r = 1 R \frac{a}{b} = \frac{1}{\frac{b}{a}} \Rightarrow r = \frac{1}{R} . As r = ( R 60 ) r = (R - 60) , ( R 60 ) = 1 R R 2 60 R 1 = 0 R = 60 + 3604 2 R = 60 + 2 901 2 m + n = 30 + 901 m = 30 (R - 60) = \frac{1}{R} \Rightarrow R^{2} - 60R - 1 = 0 \Rightarrow R = \frac{60 + \sqrt{3604}}{2} \Rightarrow R = \frac{60 + 2\sqrt{901}}{2} \Rightarrow m + \sqrt{n} = 30 + \sqrt{901} \Rightarrow m = 30 and n = 901 m + n = 931 n = 901 \Rightarrow \boxed{m + n = 931}

Note : as the correct solution (R) is of the form m + n m + \sqrt{n} , I only represented the solution R = 60 + 3604 2 R = \frac{60 + \sqrt{3604}}{2} , because the solution R = 60 3604 2 R = \frac{60 - \sqrt{3604}}{2} is not the correct one.

Same approach. But i just solved using completing square to get b:a.

Sachin Vishwakarma - 5 years, 8 months ago
Aakash Khandelwal
Oct 15, 2015

X-1/X =60 . Find X . Where X = correct answer

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...