在曲線x=t,y=t2,z=t3上某點(diǎn)的切線平行于平面x+2y+z=4,則該點(diǎn)的坐標(biāo)為:()
A.(-1/3,1/9,-1/27),(-1,1,-1) B.(-1/3,1/9,-1/27),(1,1,1) C.(1/3,1/9,1/27),(1,1,1) D.(1/3,1/9,1/27),(-1,1,-1)
設(shè)z=arccot(x+y),則zy′等于:()
A.1/[1+(x+y)2] B.-sec2(x+y)/[1+(x+y)2] C.-1/[1+(x+y)2] D.
函數(shù),在點(diǎn)(0,0)處是否連續(xù)、可導(dǎo)或可微()?
A.連續(xù)但不可導(dǎo) B.不連續(xù)但可導(dǎo) C.可導(dǎo)且連續(xù) D.既不連續(xù)又不可導(dǎo)