I don't know where I'm going wrong. The answer at the end is supposed to be "tan a= 3/4" but going through it step by step I've gone wrong but I don't know how.
You have essentially said at the beginning of the question (correctly):
In order for both sides of the equation to be equal, both sides have to have
This means that, looking at the right hand side, .
Both sides have to have .
So, looking at the right hand side,
And then it's just an application of