Question

find the points on the curve y=sinx+cosx for 0 11 years ago

Answer 1

Do you still need help?

Answer 2

So why don't you start by taking derivitive of y= sinx + cosx

Answer 3

and the slope being horizontal would mean to find y prime and set that equal to zero.

Answer 4

yes i did that but from there i get lost

Answer 5

cosx-sinx=0 then -sinx=0???

Answer 6

ok so we have y = sinx + cos x. the derivitive of sinx= cox and the derivitive of cosx= -sinx.

Answer 7

so y' or dy/dx as some write it = cosx-sinx

Answer 8

So now you will want to set that equal to zero, so what would that look like?

Answer 9

sorry I see where you had that.
cosx-sinx=0
cosx=sinx

Answer 10

Can you think of anyhere on the unit circle where the cos of an angle and the sin of an angle are equal?

Answer 11

pi/4?

Answer 12

Yeah and also 5pi/4 right?

Answer 13

where both the x and y coordinates would be negative. Quadrant III

Answer 14

right!

Answer 15

Part of the trick of this problem was recognizing that when they said find where the slope is horizontal is that that means where y'=0

Answer 16

yes i understand that where I'm having trouble is the trig that i forgot thanks!

Answer 17

No problem.