If the point P(a2,a) lies in the region corresponding to the acute angle between the lines 2y=x and 4y=x , then
a∈[2,4]
a∈(2,4]
a∈[2,5)
a∈(2,4)
But a2>0, hence point P(a2,a) lies in first quadrant. We have
a−a24>0 & a−a22<0
(∴(1,0) and P lies on same side of x-2y=0 and (1,0) and P lies opposite sides of x-4y=0)
⇒0<a and a∈(−∞,0)∪(2,∞)
⇒a∈(2,4)