...1):(1)若a//b求x的值;(2)设f(x)=a·b,x∈(0,π/2)求f(x)的值_百度...
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1)
cosx=-cos(x-π/3)
(x-π/3)+x=π+2kπ
2x=4π/3+2kπ
x=2π/3+kπ
2)
a*b=cosx*cos(x-π/3)-1
=cosx(cosx+根号3sinx)/2-1
=(2cos²x+2根号3cosxsinx)/4-1
=(cos2x+1+根号3sin2x)/4-1
=(cos2x+(根号3)sin2x)-3/4
=2sin(2x+π/6)-3/4
x~0,π/2
2x+π/6~(π/6,7π/6)
sin(π/2)=1 最大
sin(7π/6)=-1/2 最小
a*b最大值=2-3/4=5/4
最小值=-1-3/4=-7/4
