举报
橄榄和芹菜
如果f(x)=A sin(wx+π/6)
(1)根据函数图像可知,f(x)的最大值为2,即f(x)max=Asin(wx+π/6),此时sin(wx+π/6)=1,则A=2;
从图像可知当x=π/9取得最大值,把x=π/9及A=2代入f(x)=A sin(wx+π/6)得
2sin(w*π/9+π/6)=2,所以sin(w*π/9+π/6)=1,w=3.
所以f(x)=2sin(3x+π/6)。
f(2/3kπ)=2sin(3*2/3kπ+π/6)=2sin(2kπ+π/6)=2*1/2=1.
(2)f(a/3+π/9)=根号7/2,f(a/3+π/9)=2sin【3(a/3+π/9)+π/6】=2sin(a+π/3+π/6)=2sin(a+π)=-2sina,即sina=-√7/4.因为-π/2
sin(2a+π/4)=sin2acosπ/4+cos2asinπ/4
=√2/2(sin2a+cos2a)=√2(2sinacosa+cos²a-sin²a)
=√2/2【2*(-√7/4)*3/4+(9/16-7/16)】
=√2/2【-3√7/8+1/8】
=-3√14/16+√2/4
不知道第二问最后答案对不对,反正方法是这样。