Easy Trigonometry

Geometry Level 2

If sin θ \sin \theta = 1 3 \frac{1}{3} and cos θ \cos \theta > 0, The value of tan θ \tan \theta can be expressed in the form a b \frac{\sqrt{a}}{b} where a is a square free integer and b is an integer, what is the value of a+b?


The answer is 6.

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2 solutions

Squaring sin θ \sin \theta = 1 3 \frac{1}{3} , we have ( sin θ \sin \theta )^2 = 1/9.

Using the identity ( sin θ \sin \theta )^2 = 1- ( cos θ \cos \theta )^2, we have ( cos θ \cos \theta )^2= 8/9.

Simplifying, we get cos θ \cos \theta = 2 2 3 \frac{2\sqrt{2}}{3} (positive because of the condition cos θ \cos \theta >0).

Since tan θ \tan \theta = sin θ cos θ \frac{\sin \theta}{\cos \theta} , we have tan θ \tan \theta = 2 4 \frac{\sqrt{2}}{4} .

Thus, we have a= 2 and b= 4 .

Finally, we have a + b = 6 \boxed{a+b= 6} .

Very simple and good logical solution.th anks

Krishna Garg - 6 years, 6 months ago

Damnit! I forgot to rationalize the answer and thus couldn't solve the problem.

Prasun Biswas - 6 years, 6 months ago
Aliki Patsalidou
Apr 24, 2014

from pythagoras theorem we find tdat the other vertical is square root of 8 ,so tanθ equal 1 over square root of 8 so a=2 and b=4

square roor of 8 is not 4

Ali Baba - 7 years, 1 month ago

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posted wrongly, sorry

Ali Baba - 7 years, 1 month ago

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is not wrong because tanθ=1/square root of 8 which equal to 2*square root of 2 over 8 .after simplifications we haue square root of 2 /4 so a=2 and b=4

aliki patsalidou - 7 years, 1 month ago

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