Because the slope of the straight line is (1-m 2)/(2-1) =1-m 2.

Because m2 >；; =0

So 1-m 2

So the slope range is (negative infinity, 1)

The range of inclination angle is [0, pai]

The value of the corresponding tilt angle is [0, pai /4] and it is combined (pai /2, pai).