若sin2xsin3x=cos2xcos3x,0°〈x〈90°,则x的一个值是()
A: 15°
B: 18°
C: 30°
D: 36°
A: 15°
B: 18°
C: 30°
D: 36°
举一反三
- 求微分方程[img=634x60]17da653955cf9e7.png[/img]的特解。 （ ） A: sin(2*x)/3 - cos(x) - cos(x)/3 B: sin(2*x)/3 - cos(x) - sin(x)/3 C: cos(2*x)/3 - cos(x) - sin(x)/3 D: sin(2*x)/3 - sin(x) - sin(x)/3
- 1802fa0b3e3fac1.png,求y的一阶导数 A: 3sin^2(x/3) B: sin^2(x/3) C: 3sin^2(x/3)cos(x/3) D: sin^(x/3)cos(x/3)
- 已知\( y = {x^3}\cos 2x \)，则\( y'' \)为（ ）. A: 0 B: \( 6x\cos 2x{\rm{ + }}12{x^2}\sin 2x - 4{x^3}\cos 2x \) C: \( 6x\cos 2x - 12{x^2}\sin 2x{\rm{ + }}4{x^3}\cos 2x \) D: \( 6x\cos 2x - 12{x^2}\sin 2x - 4{x^3}\cos 2x \)
- 【单选题】极限 lim x → 0 1 − cos 3 x x sin 3 x 的值为? A. 0 B. 1/6 C. 2/3 D. 3/2
- $\int {{1 \over {3 + 5\cos x}}} dx = \left( {} \right)$ A: ${1 \over 4}\ln \left| {{{2\cos x + \sin x} \over {2\cos x - \sin x}}} \right| + C$ B: ${1 \over 4}\ln \left| {{{2\cos {x \over 2} + \sin {x \over 2}} \over {2\cos {x \over 2} - \sin {x \over 2}}}} \right| + C$ C: $\ln \left| {{{\cos {x \over 2} + \sin {x \over 2}} \over {\cos {x \over 2} - \sin {x \over 2}}}} \right| + C$ D: $\ln \left| {{{\cos x + \sin x} \over {\cos x - \sin x}}} \right| + C$