Can somebody please explain to me why the answer to $\displaystyle 5b^4=194$ is ±2.5 and not just 2.5 and why the answer to $\displaystyle \frac{b^7}{b^4}=\frac{75}{4}$ is 2.66 and not ±2.66 ?

Hopefully you understand where my confusion is... it's about ± and when it should and shouldn't be used.