(0<m<π)在x=π处取最小值
(1)求m的值,(2)在△ABC中,a、b、c分别是角A,B,C的对边,已知a=1,b=根号2,f(A)=根号3/2,求角C
(0<m<π)在x=π处取最小值
(1)求m的值,(2)在△ABC中,a、b、c分别是角A,B,C的对边,已知a=1,b=根号2,f(A)=根号3/2,求角C
1)f(x)=2sinxcos²(m/2)+cosxsinm-sinx
=2sinx[(1+cosm)/2]+cosxsinm-sinx
=sinx+sinxcosm+cosxsinm-sinx=sin(x+m)
x=π处取得最小值, ∴π+m=3π/2+kπ, m=π/2+kπ
0<m<π, ∴m=π/2
2)f(x)=sin(x+π/2)=cosx, f(A)=cosA=√3/2, ∴A=π/6,sinA=1/2
正弦定理:a/sinA=b/sinB, 1/(1/2)=√2/sinB, ∴sinB=√2/2, B=π/4或3π/4
∴C=π-A-B=π-π/6-π/4=7π/12, 或C=π-A-B=π-π/6-3π/4=π/12
综上,C=π/12, 或7π/12