3(a) 老師叫我們用 dy/dx>0 然後用ax^2+bx+c>0 completing the square
to get the a(x^2+b/2a)^2+C-b^2/4a>0
then therefore: C-b^2/4a>0
b^2-4ac>0
thus the solution is always increasing and have no turning point
u see this right or not >>>>>????
as the dy/dxnot equal to 0 then no turning point