Trig problem
Prove
\[\sin\left(\arctan\frac{y_2}{x_2}-\arctan\frac{y_1}{x_1}\right)\sqrt{x_2^2+y_2^2}\sqrt{x_1^2+y_1^2}=x_1y_2-x_2y_1.
\]
You may assume \(\text{sgn}(x_1x_2)=1\).
How to do this?
Prove
You may assume \(\text{sgn}(x_1x_2)=1\).
How to do this?
