又 一條數題

sin2θ=0.5
sin2θ=sin30
2θ=30 or 180-30 or 360+30 or 540-30
θ=15 or 75 or 165 or 255

2008-03-28 15:47:17 補充：
sorry, 165=>195

2008-03-28 15:53:35 補充：
For mashi_yuki29:
Because it is sin2θ
0<=θ>=360
0<=θ>=720

equation:sin2θ=0.5(0°&lE;θ&lE;360°)
sin2θ=0.5
2θ=π/6+2kπ

2 個roots

sin2θ=1/2
2θ=30 or 2θ=150
θ=15 or θ=75