未知类型:{'options': ['10sin(62.8t+[img=20x15]17e436158120103.jpg[/img])', ' 10[img=21x20]17e43630963ca84.jpg[/img]sin(62.8t+[img=20x15]17e436158120103.jpg[/img])', ' 10[img=21x20]17e43630963ca84.jpg[/img]sin(62.8t+[img=20x15]17e43aa0991ff38.jpg[/img])', ' 10cos(62.8t+[img=20x15]17e436158120103.jpg[/img])'], 'type': 102}
举一反三
- 用戴维南定理求(a)中的电流向量I2[img=960x518]17e43aa0a588832.jpg[/img] 未知类型:{'options': ['2[img=21x20]17e43630963ca84.jpg[/img]∠-[img=20x15]17e43aa0ae535b8.jpg[/img]', ' 2.5[img=21x20]17e43630963ca84.jpg[/img]∠-[img=20x15]17e43aa0ae535b8.jpg[/img]', ' 2∠-[img=20x15]17e43aa0ae535b8.jpg[/img]', ' 2.5[img=21x20]17e43630963ca84.jpg[/img]∠[img=20x15]17e43aa0ae535b8.jpg[/img]'], 'type': 102}
- 正弦交流电流的频率为50Hz,有效值是1A,初相角90°,其瞬时值表达式为()。 未知类型:{'options': ['i(t)=sin(314t+90°)A', ' i(t)=[img=21x20]17e43630963ca84.jpg[/img]sin(314t+90°)A', ' i(t)=cos(314t+90°)A', ' i(t)=[img=21x20]17e43630963ca84.jpg[/img]cos(314t+90°)A'], 'type': 102}
- 求不定积分[img=132x48]17da6537fc8dad6.png[/img]; ( ) A: -(4*(cos(x/2)/2 + 2*sin(x/2)))/(17*exp(2*x)) B: (4*(sin(x/2)/2 + 2*sin(x/2)))/(17*exp(2*x)) C: (4*(cos(x/2)/2 + 2*sin(x/2)))/(17*exp(2*x)) D: (4*(cos(x/2)/2 + 2*cos(x/2)))/(17*exp(2*x))
- 已知[img=138x19]17e43f8966ee7a8.jpg[/img]A,[img=150x19]17e43f896f977b9.jpg[/img]A,则( )。 未知类型:{'options': ['17e43efebd80a36.jpg超前[img=10x17]17e438b794b2283.jpg[/img][img=20x15]17e43aa0991ff38.jpg[/img]', ' [img=10x17]17e43efebd80a36.jpg[/img]滞后[img=10x17]17e438b794b2283.jpg[/img][img=20x15]17e43aa0991ff38.jpg[/img]', ' 相位无法判断'], 'type': 102}
- 求微分方程[img=143x21]17da5f14490e50e.png[/img]的通解,实验命令为(). A: dsolve(D2y-2*Dy+5*y=sin(2*x),x)ans =exp(x)*sin(2*x)*C2+exp(x)*cos(2*x)*C1+1/17*sin(2*x)+4/17*cos(2*x) B: dsolve('D2y-2*Dy+5*y=sin(2*x)','x')ans =cos(2*x)*(sin(4*x)/17 - cos(4*x)/68 + 1/4) - sin(2*x)*(cos(4*x)/17 + sin(4*x)/68) + C1*cos(2*x)*exp(x) - C2*sin(2*x)*exp(x) C: dsolve(D2y-2*Dy+5*y=sin(2*x),'x','y')ans =exp(x)*sin(2*x)*C2+exp(x)*cos(2*x)*C1+1/17*sin(2*x)+4/17*cos(2*x)
内容
- 0
已知某正弦量的有效值相量为30∠-30°V,电路的频率为f=50Hz,则该正弦量的瞬时值表达式为() 未知类型:{'options': ['30cos([img=62x17]17e43c56178eac7.jpg[/img])', ' 30[img=21x20]17e43630963ca84.jpg[/img]cos([img=62x17]17e43c56178eac7.jpg[/img])', ' 30[img=21x20]17e43630963ca84.jpg[/img]cos([img=71x17]17e43c561fd2fbf.jpg[/img])', ' 30[img=21x19]17e435c1ed35b3d.jpg[/img]cos([img=71x17]17e43c561fd2fbf.jpg[/img])'], 'type': 102}
- 1
一个正弦量可以用相量来表示,所以有等式i1 =[img=21x20]17e43630963ca84.jpg[/img]sin (100 πt – 90o) A = 1∠-90oA。
- 2
已知随机变量X的分布列如下:[img=386x130]17e43ec4c459e73.png[/img],则E(X)= A: 17/30 B: m未知,无法求出 C: -30/17 D: -17/30
- 3
已知u=10sin(314t-[img=8x11]17e435c54b0e71f.jpg[/img]/3)V,i=10[img=21x20]17e43630963ca84.jpg[/img]sin(314t+[img=8x11]17e435c54b0e71f.jpg[/img]/2)A,电压与电流的相位差[img=45x16]17e447252d78810.jpg[/img]是( )度,即( )超前( ).
- 4
已知平稳随机过程X(t)的自相关函数为[img=274x28]18034a95f55be83.png[/img],则X(t)的均值为? A: 0 B: 10 C: -10 D: [img=32x20]18034a95fdece56.png[/img]