Chapter 6 - Inverse Circular Functions and Trigonometric Equations - Section 6.4 Equations Involving Inverse Trigonometric Functions - 6.4 Exercises - Page 285: 11

$x=4$ $arccos(\frac{y}{6})$

$y=6 cos\frac{x}{4}$ Need to solve $x$ in order to find this divide the above equation by 3 both sides. $cos\frac{x}{4}=\frac{y}{6}$ Apply definition of arccosine. $\frac{x}{4}=arccos(\frac{y}{6})$ $x=4$ $arccos(\frac{y}{6})$