- #1
Feodalherren
- 605
- 6
Homework Statement
All solutions in the interval 0 ≤ x < 2∏
Sin 2x = -2cos x
The Attempt at a Solution
I went about it in two different ways.
The first way:
I simply used the double angle formula to get
2sinx cosx + 2cos x = 0
From this we get that whatever makes cos x = 0 will make the whole equation 0.
There are two answers within the interval; ∏/2 and 3∏/2.
This is the correct solution.
When I was studying for my midterm I went about it in a different way though, and I only got one solution. I was wondering what I was doing wrong as it seems to be all legal algebra to me.
2sinx cosx = -2 cos x
divide both sides by cos x
2sinx = -2
divide by 2
sin x = -1
This only gives me one solution, 3∏/2.
What am I doing wrong?