The absolute value of a number is always positive. EVERY value of 'w' has an absolute value greater than -0.4 . EVERY number is a solution to the equation. There are an infinite number of them.
The photo is an example. Divide the diameter by 2 to get the radius. Then times 1/3 time Pi times the radius squared times the height. The formula is V=1/3(Pi)(radius squared)(height)