This article describes how to change your settings to fix the missing minus symbols in the eBook. 

If you find your eBook is missing math symbols in equations, you can resolve this issue with the following steps:

  1. Choose as a right click with your mouse any math problem on the page in the eBook to change the math settings. 
    Note: for tablets a right click is usually a tap and hold onto the screen.
  2. Choose "math renderer"
  3. Choose "HTML-CCSS" 

These settings on your device will remain until changed. See example below.