sin2x=1/2,所以2x=30°或150° 则 x=15°或75° sin15° =sin(45°-30°） =（1/2)√2 x(1/2)√3-(1/2)√2 x(1/2) =(1/4)(√6 -√2) sin75° =sin(45°+30°） =（1/2)√2 x(1/2)√3+(1/2)√2 x(1/2) =(1/4)(√6 +√2)
