2 1: 1/2,
22: two thirds and three,
23: 3,
24:2,
25:cosπ/9
26:( 1)
、 ∵ 3>2
∴f(3)=2X3=6
∵-25
∴f(4)=2X4=8
That is, f[f(-2)]=8
(2)、
If a≥2, then 2a= 16 a=8.
If a < 2, then the square of a = 16.
A= plus or minus 4 (minus 4)
To sum up, A is 8 or -4.
27: Because BB 1 is a cylindrical bus, BB 1 is perpendicular to ABC, so BB 1 is perpendicular to AC, and because AB is the diameter in the bottom circle, AC vertical BCBC intersects BB 1 at B, so sum AC vertical plane BB1C.