To be specific, donīt mix the power-required graph with the thrust-required. They might look similar or even be wrongly simplified to be the same but it is a difference.
The thrust required is the same curve as total drag vs speed (where you find the speed for best glide in the bottom)
The power required curve looks similar but with the minimum point at a lower speed. It also appears to be somewhat "tilted" anticlockwise due to the influence of speed.
(To get a P-req diagram just take a T-req and multiply all the points of the curve with their own speed)
This makes the high speed part of the curve increase even faster than in the T-req but flattens out the penalty at lower speeds.
To find Vx you have to look in a Thrust-availible vs Thrust-required (Vx = max diff)
For Vy it have to be Power-availible vs Power-required ( Vy = max diff)
Its important that all comparisons is made in the same type (power or thrust).
Another trick is to keep the whole prop vs jet question out of the question until you understand this part of it since it is very easy to start mixing stuff up then.
Hope I didnīt confuse you more,
