State the limits for B if given that B is an obtuse angle and
a) tan2B is negative
b) tan4B is positive
c) tan2B is negative or tan 4B is positive
It is clear to me that you don't understand much of this, do you?
From the given it must be true that . Thus any answer you find must be in that range.
If then or , which is in that range.
If then it could be or , which is NOT in that range.
So we must take another course.
Suppose that or then .
Solving we get , which is in the range.