How do we get rid of z? Well, if we are on the top surface, z So, I plug z equals z2 of x, y into the formula for R, whatever it may be.
怎样才能消去z？，考虑顶部曲面，通过函数z2给出。，z，is，given，by，this，formula，，z2，of，x，，y。,所以我把z=z2代入到R中，不管是什么。
Remember that polar coordinates are about replacing x and y as coordinates for a point on a plane by instead r, r and theta,which is the angle measured counterclockwise from the positive x-axis.
极坐标是关于r，θ的,用r，θ代替平面上一点的x，y坐标，是从原点到那一点的距离，，which，is，the，distance，from，the，origin，to，a，point，θ是由x轴逆时针旋转,而得到的夹角。
So, when you go to polar coordinates, basically all you have to remember on the side of integrate is that x becomes r cosine theta. y becomes r sine theta.
在极坐标系里，要记住在积分一侧,只是把x变成rcosθ，y变成rsinθ
Or, the other way around, I have a function of x and y and I want to express it in terms of the polar coordinates r and theta.
反过来，有一个关于x和y的函数,也可以表示成极坐标r和θ
We want to know whether a given vector field with components P, Q and R can be written as f sub x, f sub y and f sub z for a same function f.
要看向量场,能否写成，其中f是同一个函数。
Besides that, we presents the gravitational wave energy density under the weak field situation and gives the x - y plane numerical calculation to curvature scalar R and energy density .
还有计算了在弱场条件近似下引力驻波的能量密度，并给出曲率标量R和能量密度平面的数值计算。
Hu G. L., X. y. lu, J. G. Wu, S. R. Shao and C. H. Shi, Direct Determination of Total Flavones in Ginkgo Extract Powder by Near-infrared Diffuse Reflection Spectroscopy.
胡钢亮、吕秀阳、吴建国、邵胜荣和石春海，近红外漫反射光谱法直接测定银杏提取物粉末中总黄酮的含量。
Yang X Y, Liu G S, WU R J, et al. Effects of shading at different growth, development and quality of tobacco[J]. Chinese Journal of Ecology, 2007,26(7):1014-1020.
杨兴有，刘国顺，伍仁军，等。不同生育期降低光强对烟草生长发育和品质的影响[J]。生态学杂志，2007，26（7）：1014-1020。
Yang X Y, Liu G S, WU R J, et al. Effects of shading at different growth, development and quality of tobacco[J]. Chinese Journal of Ecology, 2007,26(7):1014-1020.
杨兴有，刘国顺，伍仁军，等。不同生育期降低光强对烟草生长发育和品质的影响[J]。生态学杂志，2007，26（7）：1014-1020。
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