Question

HELP.
Find the exact value of the expression, if it is defined.

cos(cos-1 2/3)

Answer 1

The cos and cos inverse "undo" each other. Leaves you with 2/3.

Answer 2

my teacher told me not to do it like that, and to actually solve it. how would i do it then?

Answer 3

Sound advice from your teacher :)

OK. Starting with the inside function, cos inverse (2/3).

The inverse cosine function is defined only from 0 to pi.

You need a calculator to find the value of cosine inverse (2/3).

Can you do that? Then we can proceed.

Answer 4

lol yeah!
.84107

Answer 5

haha. COOL.

The cosine inverse function is read as:

The angle whose cosine is (2/3).

That means your calculator gave you an ANGLE.

Now you need to evaluate the outer function (the cosine) at the angle you got using your calculator.

Answer 6

haha soo .785887?

Answer 7

Ummm. For cos inverse (2/3), I get 48.1896851

Answer 8

Double check your calculator please.

Answer 9

is urs in radians?

Answer 10

Mine is in degrees. You can find in radians or in degrees. Depends on what they are asking I guess.

Answer 11

i thought we had to use it in radians?

Answer 12

In radians, I am getting .6666666667. Final answer

Answer 13

how do you find the final?

Answer 14

I checked it both ways. You get the same answer. Make sure to specify your units.

Answer 15

OH.

You found the cosine inverse (2/3). Now you have to find the cosine of that value.

cos(cos inverse (2/3).

See, we did the "inner" problem. Got an answer. We still have to evaluate the outer problem.

Answer 16

okay so now what do we need to do?

Answer 17

So you need to find

cos(.8410686706)

Answer 18

Which is .6666666667

Which is also 2/3 (what I said at the beginning).

:)

Answer 19

Now gimme a prize! lol

Answer 20

loll thankss!! :)))

Answer 21

Sweet! Thanks and smell ya later ;)

Answer 22

LOL smell ya later

Answer 23

thanks! :)