3x3决定因素 - 问题2

让我们计算更多的决定因素。这次我选择了两个特殊的。请注意，相隔A的决定因素与第b部分非常相似。只有前两排正在更改，我希望看到它的效果是在决定因素的价值上。

无论如何，让我们从第一个开始。请记住我之前所说的，您可以沿任何行或列扩展决定因素。沿着0的行或列扩展真的很好。所以我要沿着那行扩展这个。

第二行，两个0的将使这真的很容易。所以沿着第二行扩展，我必须记住我需要使用这些标志;减去加号。所以从2开始，所以减去2次，然后将次要的助理与2将是-7 3 1 6.然后当然加0减0，它将是其他一些决定因素的0倍，减去0 times some other determinant doesn’t matter. Those are just going to zero out, so this will be a lot easier having it done along this row.

SO-2次-42减去3.这是-45次-2是90.漂亮和简单。现在在这个例子中，我在顶行中得到了我的0。所以我要沿着顶级展开。这将给我和沿着它的顶部排水加上的顶部。

您知道另一种记住加号或减去的方法是占用行和列号并将其添加。Like this entry 2, is row 1 column 1 1 plus 1 is 2. Whenever you got an even result, use a plus sign, whenever you got an add result use a minus sign, that’s another way to figure out what the sign is going to be. In this case it’s going to be plus. Plus 2 times the determinant -7 3 1 6, minus 0 times some determinant. Write this guy times its minor, this guy times its minor, doesn’t matter what its minor is. Plus 0 times that determinant. Those are going to zero out and I’ll just get 2 times -42 minus 3. So that’s 2 times -45 or -90. So I got -90 for this answer and 90 for this one. That tells me that the result of switching two rows, has the effect of changing the sign of the determinant.