Question

How is cos x -x(sin x) the same as cos x-x?

Answer 1

who said it was?

Answer 2

Im looking to the derivative of (x) (cos x)
Using the Product Rule I get:
(1) (cos x) + (x)(-sin x)

Book says answer is cos x -x

Answer 3

the textbook cut off the sinx. you answer is right.

you'll see that textbooks are filled with mistakes :P

Answer 4

certainty: 100%

you can even try it with your calculator (make sure it's in radians)

Answer 5

thanks @Euler271! Glad i'm not crazy, I was here trying to find the answer!

Answer 6

I tried it with the calculator the first time, but i didnt realize it was in degrees, not radians so i was even more confused lol

Answer 7

lol :P

ya. textbooks have made me doubt my sanity too. i've wasted hours on problems before only to find out i was right.

glad i could help ^_^