In a survey work, three independent angles $X, Y$ and $Z$ were observed with weights $W_X, W_Y, W_Z$,respectively. The weight of the sum of angles $X, Y$ and $Z$ is given by:

- $1/ \big( \dfrac{1}{W_X} + \dfrac{1}{W_Y} + \dfrac{1}{W_Z} \big) \\$
- $\big( \dfrac{1}{W_X} + \dfrac{1}{W_Y} + \dfrac{1}{W_Z} \big) \\$
- $W_X +W_Y+W_Z \\$
- $W_X^2 +W_Y^2+W_Z^2$