Question

Rewrite with only sin x and cos x.

cos 3x

(A) cos x - 4 cos x sin2x
(B)-sin3x + 2 sin x cos x
(C)-sin2x + 2 sin x cos x
(D)2 sin2x cos x - 2 sin x cos x

Answer 1

Hint
cos 3x = cos(2x + x)

Answer 2

Ye s I know that.

Answer 3

I have a headache from a slip and fall accident and just don't feel like working. I will medal you if you have the correct answer.

Answer 4

but I dont think we can use that anyway
because cos ( a + b) = cosa cosb - sina sinb

Answer 5

-_-

Answer 6

So can someone please tell me the answer

Answer 7

Its not C because that simplifies to -sin 2x + sin2x = 0

Answer 8

ohkay

Answer 9

I know it's not D because I chose that and it was wrong

Answer 10

I cant convert cos 3x into any of the options . I think there might be an error in the question.

I'll plug in x = 20 degrees and see if any of them work out to 0.5
(because cos 60 = 0.5)

Answer 11

try B then

Answer 12

- sin 60 + 2 cos 20 sin 20 = -0.2232

not that one

Answer 13

nor A - none of them equal cos 3x

Answer 14

thers a problem with the question

Answer 15

That's the beauty of Virtual School

Answer 16

Try https://www.symbolab.com/solver/trigonometric-identity-calculator

Answer 17

I know it's not D or B, because I just got it wrong and can't do it over again. I have been told it's not A or C by an elite, and I KEEP GETTING THE QUESTION WRONG!!!!