题目规定：sin(−x)=−sinx\sin(-x)=-\sin xsin(−x)=−sinx，cos(−x)=cosx\cos(-x)=\cos xcos(−x)=cosx，cos(x+y)=cosxcosy−sinxsiny\cos(x+y)=\cos x\cos y-\sin x\sin ycos(x+y)=cosxcosy−sinxsiny，给出以下四个结论：(1)sin(−30°)=−12(1)\sin(-30°)=-\dfrac{1}{2}(1)sin(−30°)=−21；(2)cos2x=cos2x−sin2x(2)\cos 2x=\cos^{2}x-\sin^{2}x(2)cos2x=cos2x−sin2x；(3)cos(x−y)=cosxcosy+sinxsiny(3)\cos(x-y)=\cos x\cos y+\sin x\sin y(3)cos(x−y)=cosxcosy+sinxsiny；(4)cos15°=6−24.(4)\cos 15°=\dfrac{\sqrt{6}-\sqrt{2}}{4}.(4)cos15°=46−2.其中正确的结论的个数为()(\quad)()A.111个 B.222个C.333个D.444个知识点：互余两角三角函数的关系章节：图形的变化 / 锐角三角函数
