Normally you would not use the quadratic formula to do this 
because it is easier to do by factoring.  However when you
are instructed to use a certain method, you must use it.

-2x² + 5x = 0

Write it with a +0 at the end of the left side:

-2x² + 5x + 0 = 0, so it can be compared to
 ax² + bx + c = 0

and we can see that a=-2, b=5 and c=0.

Then we write the quadratic formula:



and substitute:



Then simplify:







We use the + sign







So 0 is one solution.

We use the - sign:







So  is the other solution.

Edwin