Hi my question is what approach i should use in order to solve this $\cos(\theta +20) = -0.74$?
and why do we get rid of the negative sign when solving basis angle?
Here is my working
$\cos(\theta +20) = -0.74$
Then, $\alpha+20 = \arccos (0.74)$, to find the basis angle. After I plugged into the calculator and got $42.3$, I subtract $20$ from $42.3$ to solve for $\theta$ which is $22.3$. $\theta = 42.3 -20 = 22.3$
Since $\cos$ is negative, the angle is at 2nd and 4th quadrant. So I solve for the angle $180-22.3=157.7$ and $180+22.3=202.3$
But all of this is wrong can someone explain? I think it is my approach that got me wrong, but I am unsure.