Let's consider the tangent addition formula:
tan(a+b)=1−tan(a)tan(b)tan(a)+tan(b) We have the expression tan(x)cot(9∘)+tan(5x). Since cot(9∘)=tan(9∘)1, we can rewrite the expression as: tan(9∘)tan(x)+tan(5x). If the original problem asks to simplify the expression tan(9∘)tan(x)+tan(5x), it is not clear what could be simplified further. Let us try to consider a scenario where this is equal to a tangent of a sum: Let's suppose tan(9∘)tan(x)+tan(5x)=tan(a+b) Assume we want to get an identity of the form tan(A)=tan(x)cot(9∘)+tan(5x) for some A. Consider the tangent addition formula tan(a+b)=1−tan(a)tan(b)tan(a)+tan(b) We rewrite the expression as:
tan(x)cot(9∘)+tan(5x)=tan(9∘)tan(x)+tan(5x) Multiplying by tan(9∘), we get tan(x)+tan(5x)tan(9∘) If we set x=9∘, then the expression becomes tan(9∘)cot(9∘)+tan(5⋅9∘)=1+tan(45∘)=1+1=2 Suppose the original question asked to evaluate the expression when x = 9∘. Then, tan(9∘)cot(9∘)+tan(5⋅9∘)=tan(9∘)tan(9∘)1+tan(45∘)=1+1=2. Let's assume we are supposed to find when tan(x)cot(9∘)+tan(5x)=tan(6x+9∘). Using tan(6x+9∘)=1−tan(6x)tan(9∘)tan(6x)+tan(9∘)=tan(x)cot(9∘)+tan(5x)=tan(9∘)tan(x)+tan(5x), Then we would have
1−tan(6x)tan(9∘)tan(6x)+tan(9∘)=tan(9∘)tan(x)+tan(5x)tan(9∘) tan(9∘)(tan(6x)+tan(9∘))=(1−tan(6x)tan(9∘))(tan(x)+tan(5x)tan(9∘)) tan(9∘)tan(6x)+tan2(9∘)=tan(x)+tan(5x)tan(9∘)−tan(x)tan(6x)tan(9∘)−tan(5x)tan(6x)tan2(9∘) This becomes complex.