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We notice that the value of E at r naught is negative, as it should be. It's a negative number.
我们主要到在r圈时E的值为负，和它本来的值一致，是一个负数。
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And one common way to think about it, is to think about the value of r, or the radius, below which 90% of that electron density is going to be contained.
而通常的想法，是想象，r，的值，也就是半径的值，即有百分之九十的电子密度,都落在这个范围之内。
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Generally, if it pays c dollars for every period, the present value is c/r.
推广开来,如果在每段时期内支付c美元,那么它的现值就是c/r
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We'll introduce in the next course angular nodes, but today we're just going to be talking about radial nodes, psi and a radial node is a value for r at which psi, and therefore, 0 also the probability psi squared is going to be equal to zero.
将会介绍角节点,但我们今天讲的是，径向节点，径向节点就是指，对于某个r的值,当然，也包括psi的平方，等于,当我们说到s轨道时。
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We call that a node, r and a node, more specifically, is any value of either r, the radius, or the two angles for 0 which the wave function, and that also means the wave function 0 squared or the probability density, is going to be equal to zero.
节点就是指对，于任何半径，或者，两个角度,波函数等于，这也意味着波函数的平方或者概率密度,等于，我们可以看到在1s轨道里。
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If you had a perpetuity, which paid C/2 forever, you already know from the perpetuity formula that the value of that would be C/2 divided by r/2 if r/2 is the discount rate.
如果你有一只永续债券,每半年付息C/2,没有到期日,从永续债券的公式可以知道,债券价格等于C/2除以r/2,r/2为贴现率
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But instead in this chemistry course, I will just tell you the solutions to differential equations. And what we can do is we can start with some initial value of r, and here I write r being ten angstroms. That's a good approximation when we're talking about atoms because that's about the size of and atom.
但在这个课里，我会直接，告诉你们微分方程的解,我们可以给距离r一个初始值,我这里把r取10埃,当我们讨论原子时,这是一个很好的近似,因为原子的尺寸。
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g has to be less than r for this to make sense because if g--if it's growing faster than the rate of interest, then this infinite series will not converge and the value would be infinite.
必须小于r才行得通,因为如果g比利率涨的还快,那么这个无穷序列就不会收敛,价值就是无穷了
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