mgarcia634
Find all solutions in the interval [0, 2π).
cos2x + 2 cos x + 1 = 0



This Question is Closed

mgarcia634
Best Response
You've already chosen the best response.
0
cos^2 x+ 2 cos x +1=0

cwrw238
Best Response
You've already chosen the best response.
1
this is a quadratic equation which will factorise

Stiwan
Best Response
You've already chosen the best response.
1
\[\cos²(x) + 2\cos(x) + 1 = (\cos(x) + 1)²\] Hence the roots are all x out of [0,2pi) for which cos(x) = 1. pi and pi

Stiwan
Best Response
You've already chosen the best response.
1
Sorry, of course it's just + pi as there are no negative numbers in this interval

cwrw238
Best Response
You've already chosen the best response.
1
what about 0 as a solution?

cwrw238
Best Response
You've already chosen the best response.
1
no sorry  its 1

cwrw238
Best Response
You've already chosen the best response.
1
cos 0 = 1 of course

mgarcia634
Best Response
You've already chosen the best response.
0
the answer choices are a) x=2pi B)x=pi c) x=pi/4, 7pi/4

cwrw238
Best Response
You've already chosen the best response.
1
are you sure you have the correct question
is it cos 2x or cos^2 x ?

mgarcia634
Best Response
You've already chosen the best response.
0
it is cos^2 x

Stiwan
Best Response
You've already chosen the best response.
1
It's B) x = pi as in my answer.

cwrw238
Best Response
You've already chosen the best response.
1
in that case the answer is as Stiwam said

mgarcia634
Best Response
You've already chosen the best response.
0
thankyou!

cwrw238
Best Response
You've already chosen the best response.
1
yw