第二类换元法 x=cost
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证一:为了方便,记x`=dx/dt,y`=dy/dt.则d²y/dx²=d(dy/dx)/dx=d(y`/x`)/dx=[d(y`/x`)/dt]/(dx/dt)=(y`/x`)`
dx/dt=(e^t)sint+(e^t)cost=(e^t)(sint+cost)dy/dt=(e^t)cost-(e^t)sint=(e^t)(cost-sint)dy/dx=(dy/dt)/(d
dx/dt=2tdy/dt=-sin(t)dy/dx=-sin(t)/2t同理:d²y/dx²=-cos(t)/2
=(1+e^t)/(2-sint)不通,看书.
∵(sint+cost)²=sin²t+2sintcost+cos²t=1+2sintcost∴x²=1+2y∴y=x²/2-1/2
(I)曲线C1的参数方程式x=4+5costy=5+5sint(t为参数),得(x-4)^2+(y-5)^2=25即为圆C1的普通方程,即x^2+y^2-8x-10y+16=0.将x=ρcosθ,y=
(costdt)/(-sintdt)=-cott再答:或-1/tant
t=arccos(1-y)x=arccos(1-y)-sin[arccos(1-y)]【sin(arccosx)=√(1-x²)】=arccos(1-y)-√[1-(1-y)²]=
需要注意的是有个隐藏条件:(sint)^2+(cost)^2=1即(sint+cost)^2-2sint*cost=1将x=cost+sint,y=sint*cost代入得x^2-2y=1,即y=(x
dy/dx=(dy/dt)/(dx/dt)=-sint/2td²y/dx²=d(dy/dx)/dx=[d(dy/dx)/dt]/(dx/dt)=d(-sint/2t)/dt/2t=
解dy/dx=(1-sint)'/(t²+cost)'=(-cost)/(2t-sint)
在平面直角坐标系中有一条曲线,其参数方程是:x=cost,y=sint.问当他的范围是0
因为csct-sint=1/sint-sint=[1-(sint)^2]/sint=[(cost)^2]/sint=cost/sint×cost=cott×cost所以∫cott·costdt=∫(c
x=sint-costy=sint+cost则:x+y=2sintx-y=-2cost所以:(x+y)^2+(x-y)^2=2再问:这个不像圆的方程啊再答:这个是圆的方程。(x+y)^2+(x-y)^
dx=(7-7cost)dtdy=(7sint)dtdy/dx=(7sint)/(7-7cost)再问:有两个答案耶,哪个是对的呀再答:我的应该是对的,当然公因子7可以约掉
解析x=acost+atsinty=asint-atcostdx=-asint+asint+atcostdy=acost-acost+atsint∴dy/dx=(acost-acost+asint)/
dy=lnt+1dx=1-sintdy/dx=(lnt+1)/(1-sint)
dy/dt=-sintdx/dt=cost∴dy/dx=-sint/cost=-tant
x-4=5cost,y-5=5sint(x-4)^2=25cos^2t,(y-5)^2=25sin^2t(x-4)^2+(y-5)^2=25(cos^2t+sin^2t)(x-4)^2+(y-5)^2
dy/dx=y'/x'=tsint/(-sint)=-t再问:在详细一点呗再答:dy/dx=(dy/dt)/(dx/dt)=(cost-cost+tsint)/(-sint)=-t