We're going to differentiate with respect to q1, the thing we're trying--our control variable, the thing we're trying to maximize the thing with respect to and set it equal to 0.

对q1求导,q1是控制变量,也就是我们想要求出的最大值,令它等于0

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I differentiate a second time and check the sign, so the second order condition, I differentiate this expression again with respect to q1.

我们对它进行二次求导然后看符号,这个式子的二阶导数,就是一阶导数再对q1进行求导

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We're going to differentiate this with respect to q1 and then what?

对q1求导之后还要做什么

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So I'm going to differentiate this object again with respect to S1,.

我们再次对S1求导

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