Question

Find Max and Min values of f(x)=cosx-sinx, given interval of -pi 13 years ago

Answer 1

What do you get when you take the derivative?

Answer 2

-sinx-cosx

Answer 3

set the derivative equal 0, and find all the possibilities

Answer 4

For a min or a max to occur, that means that the slope of f(x) equals 0. So find where f'(x)=0.

Answer 5

I did that and I'm stuck at sinx=-cosx

Answer 6

Check your unit circle. Where does the sine of x equal the opposite of the cosine?

Answer 7

at pi/4 and 3pi/4?

Answer 8

it's one of the special angle

Answer 9

you're right, dont forget it's from -pi to pi

Answer 10

so, there are 4 possibilities

Answer 11

does that mean I forgot one?

Answer 12

ohh, so 5pi/4 and 7pi/4 too. Thanks

Answer 13

no, it's -3pi/4, -pi/4, pi/4 and 3pi/4, because the interval is from -pi to pi, 5pi/4 and 7pi/4 is off the interval

Answer 14

ok