Chapter 5 - Linear Functions - 5-3 Slope-Intercept Form - Practice and Problem-Solving Exercises - Page 313: 59

$a=-0.5$

We are given $y=2ax+4$ The equation is already in slope intercept form, which is given by the formula: $y=mx+b$, where $m$ is the slope and $b$ is the y-intercept. We can see that the coefficient of the variable x would be the slope. We set this coefficient equal to the slope m that we are given: $2a=-1$ $a=\frac{-1}{2}$ $a=-0.5$