Question

Find all solutions in the interval [0, 2π)

cos2x + 2 cos x + 1 = 0

Answer 1

Wait, isn't this the same question as the last one, except it's cos instead of sin?

Answer 2

no i don't think so

Answer 3

Yeah, you can definitely factor this. that's a cos^2(x) right?

Answer 4

yea

Answer 5

remember cos^2(x)=(cosx)^2.

Just plug in something like y=cosx into the formula and factor it out like normal.

Answer 6

i got x=2pi

Answer 7

Show me your steps.

Answer 8

my bad i got x= pi/4, 7pi/4

Answer 9

wrong problem

Answer 10

\[\cos(2x) = 2\cos^2(x)-1\]
Now, you have
\[2\cos^2(x)-1 + 2 \cos(x) + 1 = 0\]
Which is similar to:
\[ax^2 + bx + c = 0\]

Answer 11

http://openstudy.com/users/tnng#/updates/50d66f20e4b069916c8491e6

Answer 12

abb0t did you read, he said it was cos^2(x) not cos(2x)

Answer 13

Didn't read.

Answer 14

so... i tried it again and i got x= pi/2, 3pi/2

Answer 15

Why don't you write out your steps and I can help you along where you need it, if you do.

Answer 16

x=pi i got it

Answer 17

Well I'm not going to offer you any help if you're not going to try the problem.