设z是由ex+ysin（x+z)=0所确定的x，y的函数，求dz

设z=e^x-2y，而x=sint，y=t³，求dz/dt

A、dx

B、dy

C、dx+dy

D、0

A、The signing of a cancellable contract in September 20X4 to supply goods in the following year on which, due to a pricing error, a loss will be made

B、The cost of a reorganisation which was approved by the board in August 20X4 but has not yet been implemented, communicated to interested parties or announced publicly

C、An amount of deferred tax relating to the gain on the revaluation of a property during the current year. Tynan has no intention of selling the property in the foreseeable future.

D、The balance on the warranty provision which related to products for which there are no outstanding claims and whose warranties had expired by 30 September 20X4.

设u=f(x₁,x₂,x₃,x₄)，x₃=g(x₁,x₂),x₄=h(x₁,x₂,x₃)，则u_x1=______

A．gradu·gradv  B．ugradv·vgradu

C．ugradv  D．vgradu

设在xOy平面上，各点的温度T与点的位置间的关系为T=4x²+9y²，试求：

(1)在点P(9，4)处沿方向角为210°的方向l的温度变化率

(2)在什么方向上，点P处的温度变化率取得最大值？并求此最大值．

设F(x+y+z，x²+y²+z²)=0，F对各变量具有一阶连续偏导数，求由F=0所确定的函数z=f(x，y)的梯度．

若z=f(x，y)在点P(x₀，y₀)处可微，则f(x，y)在点P(x₀，y₀)处沿任何方向的方向导数(  )

A．必定存在  B．一定不存在

C．可能存在也可能不存在  D．仅在x轴、y轴方向存在，其它方向不存在

试求u=e^xyz+x²+y²在点(1，1，1)处沿曲线x=t，y=2t²-1，z=t³在点(1，1，1)处切线方向的方向导数．