请教一道函数题

显示全部楼层 · 2011-2-1 21:10:14

1、f（x）＝4sin（3x+45°）； T=2π/3。2、1/根号5...

千问 · 2011-2-1 21:10:14

(1.)最小正周期为π2\3;f(x)=4sin(3x+π/4)(2.)sinα=±√5/5...

千问 · 2011-2-1 21:10:14

(!) 3x+φ=π/2 φ=π/4
A=4/1=4
f（x）＝4sin（3x+π/4）最小正周期2π/3(2)f（2α/3+π/12）=4sin（3*(2α/3+π/12)+π/4）=12/5
sin(2a+π/2)=cos2a=1-2(sina)^2=3/5
sina=±√5/5...

千问 · 2011-2-1 21:10:14

解：（1）f(x)的最小正周期T=2π/3
A=4， φ=π/4
f（x)=4sin（3x+π/4）（2）f（2α/3+π/12）=4cos2α=12/5所以cos2α=3/5又cos2α=1-2sin^2α=3/5所以sinα=±√5 / 5...

千问 · 2011-2-1 21:10:14

3π/12+φ=π/2φ=π/4A=4f(x)的最小正周期T=2π/3f(x)的解析式f(x)＝4sin(3x+π/4)f(2α/3+π/12)=4sin(2α+π/2)=4cos(2α)=12/54cos(2α)=12/5cos(2α)=3/5 sinα=±√5/5...