x y v but actually the relevant variables for your problem are u and v.

只是让f的式子变得漂亮点，，So，x，and，y，are，giving，you，a，nice，formula，for，f，实际上，与问题有关的变量是u、

youdao

OK, so this one means we keep y constant, and partial f over partial u with v held constant, similarly.

这个的意思是，保持y恒定，而这个的意思是，保持v恒定。

youdao

v gR or equal than gR, so I have here v squared, h-y which is 2g times h minus y.

的平方肯定大于，So，v，squared，must，be，larger,或等于，所以v的平方，也就是2g乘以。

youdao