cos2x为什么等于cos^2-sin^2
举一反三
- 【单选题】设y=sin(cos(x)),求 结果为:(本题10.0分) A. cos(cos(x))*cos(x)+ sin(cos(x))*sin(x)^2 B. - cos(cos(x))*cos(x) - sin(cos(x))*sin(x)^2 C. - cos(cos(x))*cos(x)^2 - sin(cos(x))*sin(x)^2 D. - cos(cos(x))*cos(x) ^2- sin(cos(x))*sin(x)
- 曲线积分$$\int_{(0,0}^{(x,y)}(2x\cos y-y^2\sin x)dx+(2y\cos x-x^2\sin y)dy=$$ A: $y^2\cos x+x^2\cos y$ B: $x^2\cos x+y^2\cos y$ C: $x^2\sin y+y^2\sin x$ D: $x^2\sin x+y^2\sin y$
- 复数z=6i的三角形式为（） A: cosπ/2+isinπ/2 B: cosπ/2-sinπ/2 C: sinπ/2+icosπ/2 D: sinπ/2-icosπ/2
- 3. $(2x\cos y-{{y}^{2}}\sin x)dx+(2y\cos x-{{x}^{2}}\sin y)dy$的原函数是 ( ) A: ${{x}^{2}}\sin y-{{y}^{2}}\sin x+C$ B: ${{x}^{2}}\sin y+{{y}^{2}}\sin x+C$ C: ${{x}^{2}}\cos y-{{y}^{2}}\cos x+C$ D: ${{x}^{2}}\cos y+{{y}^{2}}\cos x+C$
- 【单选题】化简 sin( x + y )sin( x - y ) + cos( x + y )cos( x - y ) 的结果是 A. sin 2 x B. cos 2 y C. － cos 2 x D. -cos 2 y