Trig(continued)

2)Find the solution of sin2 theta = cos theta if 0 -< theta < 180
A)30 degrees and 90 degrees
B)30 degrees and 150 degrees
C)30 degrees, 90 degrees, 150 degrees
D)0 degrees, 90 degrees, and 150 degrees

sin2 theta = cos theta
sin2 theta - 1 = 0
(sin theta + 1)(sin theta - 1)= 0
sin theta = -1 or sin theta = 1 which is B

I used the zero property

  1. 👍
  2. 👎
  3. 👁
  1. For your earlier post for this same question at 3:17 am, I said

    "for #2 I too, like Bob, was puzzled
    First of all is it

    sin 2θ = cos θ or sin2 θ = cos θ ?

    for the first one
    2sinθcosθ - cosθ = 0
    cosθ(1sinθ - 1) = 0
    cosθ=0 or sinθ=1/2
    so θ = 90º or θ = 30º or 150º for your domain, which is choice C "

    how did you get your second line???

    1. 👍
    2. 👎
  2. line: cosθ(1sinθ - 1) = 0

    should have said

    cosθ(2sinθ - 1) = 0

    1. 👍
    2. 👎
  3. Please use ^ in front of exponents. Otherwise, we cannot tell sin (2theta) from (sin theta)^2.
    Your first step is wrong, since cos theta is not necessarly equal to 1. Also, if sin theta were 1 or -1, why would the answer be B?
    I will assume you meant to write sin (2theta) and will let x be theta, to simplify typing.
    2 sin x cos x = cos x
    2 sin x = 1
    sin x = 1/2
    x = 30 or 150 degrees.

    You seem to have treated sin2theta as sin^2 theta, in your next-to-last step, but if you do that, the answer is completely different

    1. 👍
    2. 👎
  4. my question is sin 2è = cos è NOT sin2 è = cos è. I'm sorry, I didn't understand your question earlier.

    1. 👍
    2. 👎
  5. In that case the solution I just gave you above will be the correct one.

    Notice that all 3 answers work in your original equation.

    1. 👍
    2. 👎

Respond to this Question

First Name

Your Response

Similar Questions

  1. Math

    1. Let (-7, 4) be a point on the terminal side of (theta). Find the exact values of sin(theta), csc(theta), and cot(theta). 2. Let (theta) be an angle in quadrant IV such that sin(theta)=-2/5. Find the exact values of sec(theta)

  2. Trigonometry

    Let (7,-3) be a point on the terminal side of theta. Find the exact values of cos of theta, sec of theta and cot of theta?

  3. Precalculus

    Which of the following are trigonometric identities? Select all that apply (there are 3 answers). A cos^2(theta)=sin^2(theta)-1 B sin(theta)=1/csc(theta) C sec(theta)=1/cot(theta) D cot(theta)=cos/sin(theta) E

  4. Pre-Calculus

    1.) Which of the following polar equations is equivalent to the parametric equations below? x=t^2 y=2t A.) r=4cot(theta)csc(theta) B.) r=4tan(theta)sec(theta) C.) r=tan(theta)sec(theta)/4 D.) r=16cot(theta)csc(theta) 2.) Which

  1. trig

    If sin theta is equal to 5/13 and theta is an angle in quadrant II find the value of cos theta, sec theta, tan theta, csc theta, cot theta.

  2. Precalculus check answers help!

    1.) Find an expression equivalent to sec theta sin theta cot theta csc theta. tan theta csc theta sec theta ~ sin theta 2.) Find an expression equivalent to cos theta/sin theta . tan theta cot theta ~ sec theta csc theta 3.)

  3. Pre-Calculus

    Which is the polar form of the parametric equations x=5cos(theta) and y=5sin(theta) ? a. r= 5(theta) b. r= 5 c. r= 25 cos (theta) sin (theta)***** d. r= 25cos^2 (theta) + 25sin^2 (theta) Which is the polar form of the parametric

  4. trig

    Let (theta) be an angle in quadrant II such that csc(theta)=8/5 Find the exact value of tan(theta) and cos(theta).

  1. Precalculus

    Circle O below has radius 1. Eight segment lengths are labeled with lowercase letters. Six of these equal a trigonometric function of theta. Your answer to this problem should be a six letter sequence whose letters represent the

  2. Trig

    Find the exact value of sin2(theta) if cos(theta) = -sqrt 5/3 and 180 < theta < 270. A)-1/9 B)-4 sqrt 5/9 C)1/9 D)4 sqrt 5/9 B? sin^2(theta) + cos^2(theta) = 1 sin^2(theta) = 1 - cos^2(theta) sin^2(theta) = 1 - (sqrt 5/3)^2

  3. Math

    if tan theta = 3/4 and 180 degrees ≤ 0 ≤ 270 degrees determine with the aid of a complete sketch 1. sin theta 2. cos(180 +theta) 3. angle theta

  4. math;)

    What is a simplified form of the expression (sec^3 theta) - (sec theta/cot^2 theta)? a. 0 b. sec theta-tan theta c. cos theta d. sec theta***** Every time I attempt to work out this problem I end up with one. I know the answer is

You can view more similar questions or ask a new question.