It is known that Tan (a + 45) = - 1 / 2, (90

It is known that Tan (a + 45) = - 1 / 2, (90

In the first question, we use tangent expansion to get [Tan (a) + Tan (45)] / [1-tan (a) Tan (45)] = - 1 / 2, and solve Tan (a), then we can do the second question expansion