Hello, Air!

Your thinking (and your notation) is a little fuzzy . . .

It says that the sum of their

These two seem to imply that . . . . . noderivativesis zero.

We have this right triangle:Code:* * β| a * | * | x * | * α | * - - - - - - - - *

We see that and are in thesame right triangle.

. . They are: .complementary

So: .

Now differntiate . . .

. . and you'll see why the sum of thederivativesis zero.