### Home > PC3 > Chapter 5 > Lesson 5.2.5 > Problem5-124

5-124.

Sylvie needs to solve $\cos(x)=−0.3$ on a math test. She knows that $\cos^{−1}(x)$ is the inverse function for cosine, so she applies this function to both sides of the equation. This gives her $x=\cos^{-1}(−0.3)\approx1.875$. But when her test is returned, she learns she earned only partial credit on the problem.

1. Why did Sylvie only get partial credit?

There are multiple solutions.