(1)ka+b的绝对值=根号3(a-kb的绝对值),平方
k^2|a|^2+|b|^2+2ka*b=3(|a^2|-2ka*b+k^2|b|^2)
k^2+1+2a*b=3-6ka*b+3k^2
a*b=(k^2+1)/(4k)
(2)a*b=1/4(k+1/k)>=1/4*2=1/2
a*b>=1/2
最小值=1/2
a*b
=|a|*|b|*cos
=cos
=1/2
=60°
A=60°
(1)ka+b的绝对值=根号3(a-kb的绝对值),平方
k^2|a|^2+|b|^2+2ka*b=3(|a^2|-2ka*b+k^2|b|^2)
k^2+1+2a*b=3-6ka*b+3k^2
a*b=(k^2+1)/(4k)
(2)a*b=1/4(k+1/k)>=1/4*2=1/2
a*b>=1/2
最小值=1/2
a*b
=|a|*|b|*cos
=cos
=1/2
=60°
A=60°