Try this beautiful problem from Singapore Mathematics Olympiad, SMO, 2008 based on Trigonometry.
Find the value of \(\frac {tan 40^\circ tan 60^\circ tan 80^\circ}{tan40^\circ + tan 60^\circ + tan 80^\circ}\)
Trigonometry
Tan Rule
Answer: 1
Singapore Mathematical Olympiad, 2008
Challenges and Thrills - Pre College Mathematics
If you got stuck in this sum how to get started you can start by consider a general case where \(40^\circ = A\) , \(60^\circ = B\) and \(80^\circ = C\).
So , A+B+C = \( 180 ^\circ\)
\( A+B = 180^\circ - C\)
(tan (A+B) = tan \(180^\circ - C)\)............................(1)
Now try to implement the basic formula and try to do this sum..................
In this we can continue from the last hint:
the formula of tan (A + B) = \(\frac {tan A + tan B}{1- tan A . tan B}\)
From the equation (1) .......
tan (A+B) = tan (180 - C)
\(\frac {tan A + tan B}{1- tan A . tan B} = tan (180^\circ - c)\)
(frac {tan A + tan B}{1- tan A . tan B} = -tan C )
Now just rearrange this expression and you will get the final answer.................
Here is the final solution:
{tan A + tan B} = -tan C {1- tan A . tan B}
tan A + tan B = - tan C + tan C tan A tan B
tan A + tan B + tan C = tan A tan B tan C
\(\frac {tan A tan B tan C}{tan A + tan B + tan C} = 1\)
Which is the given question. It can be a proof also...................
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