Prove that: (cos20°- sin20°)/(cos20° +sin20°} = tan25° 
Answer:

Trigonometric Ratios of Compound Angles | SciPiPupil

We already have been discussing about compound angles in previous blog posts. 

And I think it's fair not to explain everything in detail.

Rather, let's know that tan(45°-A) = (1+tanA)/(1-tanA)

We know,

Tan(A-B)= $\dfrac{tanA-tanB}{1+tanA.tanB}$


When you replace A with 45° and B with A, you will get the required formula as stated before!
Now, if you use the proper algebraic process to solve this question you will get that your RHS is equal to the LHS of the question.

Question: Prove that: (cos20°- sin20°)/(cos20° +sin20°} = tan25°| Trigonometric Ratios of Compound Angles | SciPiPupil

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