00:01
For two lines to be perpendicular to each other, we know that the slopes of the lines have to be a negative reciprocal of each other.
00:09
So, for example, if we have this first line for y equals a over b times x, where the slope is a over b, we know the line y equals negative b over a, x, is perpendicular to this first line because the slope is a negative reciprocal.
00:28
So if we use implicit differentiation on our equation of a circle here, which is x squared plus y squared equals r squared, this is a radius.
00:40
We use implicit differentiation.
00:43
We get d d d d x of x squared by the power rule is 2x.
00:49
D d d x of y squared is 2 y because y is a function of x that's times d y d y d x.
00:55
Then is equal to 0 because r squared is just a constant and d d x of a constant is 0.
01:03
If we subtract 2x on both sides, we see that 2y, d, y, d, x is equal to negative 2x...