3/4π? w=kπ+π/2，k∈Z。

w=4K/3+2/3，k∈Z

Function f (x) = coswx (w >; 0) is a monotone function in the interval 0, π/2,

X∈0，π/2，wx∈0，wπ/2。

When the monotone interval length of cosine function with zero on the right side of the origin is the largest, the interval is 0, π.

Because the function f (x) = coswx (w >; 0) is a monotone function in the interval 0, π/2,

So 0, wπ/2 is included in 0, π,

That is, wπ/2≤π and w≤2.

W=4K/3+2/3，k∈Z .

So when k=0, w=2/3.

W=2 when K= 1.