posted by Jess

How would you solve this trig function:


how do you know what trig identities to use?

  1. Damon

    cos 2x = cos^2 x - sin^2 x identity

    so we really have
    cos^2 x - sin^2 x = sin^2 x - 2

    cos^2 x = 2 (sin^2 x-1)
    but sin^2 x = 1 - cos^2 x
    so we have
    cos^2 x = 2 (-cos^2 x)
    3 cos^2 x = 0
    well cos of Pi/2 (90deg) or 3 pi/2 (270 deg) = 0

  2. drwls

    1 - 2sin^2x = sin^2x -2
    3 sin^2x = 3
    sin^2x = 1
    sinx = +1 or -1
    x = pi/2 or 3 pi/2

  3. Jess

    oh i get it.... how do you know what identities to use? did you memorize them?

  4. drwls

    The only ones I have memorized are
    cos 2x = cos^2x - sin^2 x
    sin 2x = 2 sinx cosx,
    and cos^x + sin^2 x = 1.
    I have an old book with many others that I keep handy.

Respond to this Question

First Name

Your Answer

Similar Questions

  1. Trig Identities

    Please help...I'm not understanding trig identities and how to manipulate and express these two problems in their associated functions. Thanks a)Express as a function of cos (theta) 2 sin^2(theta) - 1 b)Express as a function of sin …
  2. Trig--check answer

    Solve the equation of the interval (0, 2pi) cosx=sinx I squared both sides to get :cos²x=sin²x Then using tri indentites I came up with cos²x=1-cos²x Ended up with 2cos²x=1 Would the answer be cos²x=1/2?
  3. Trigonometry

    Use the trig Identities to find the other 5 trig functions. Problem 7.)Tan(90-x)=-3/8 8.)Csc x=-13/5 9.)Cot x=square root of 3 10.)Sin(90-x)=-.4563 11.)Sec(-x)=4 12.)Cos x=-.2351 I need HELP!
  4. trig 26

    simplify to a constant or trig func. 1. sec ²u-tan ²u/cos ²v+sin ²v change expression to only sines and cosines. then to a basic trig function. 2. sin(theta) - tan(theta)*cos(theta)+ cos(pi/2 - theta) 3. (sec y - tan y)(sec y + …
  5. trig

    combine fractions and simplify to a multiple of a power of a basic trig. function.?
  6. trig

    Solving Trig Functions: How Do You Solve For Sin 7.5 Using Half-Angle and Double-Angle Identities?
  7. Trig

    If sinx = 1/4 Find the exact value of cos2x I used the formula for double angle identities : cos2x = 1-2sin^2x and got the answer 1/2 The book says the answer is 7/8 How would they get to that conclusion?
  8. trig

    I keep trying to find the power reducing formula for sin^4(x), but I can't seem to get all the fractional parts correct. The answer I should be getting is: sin^4(x)=(1/8)cos4x-(1/2)cos2x+(3/8) I can only get this far knowing feeling …
  9. Precalculus/Trig

    I can't seem to prove these trig identities and would really appreciate help: 1. cosx + 1/sin^3x = cscx/1 - cosx I changed the 1: cosx/sin^3x + sin^3x/sin^3x = cscx/1-cosx Simplified: cosx + sin^3x/sin^3x = cscx/1-cosx I don't know …
  10. Trig identies, Calculus

    Use the identities cos^2 x + sin^2 x =1 and cos2x=cos^2 x -sin^2 x to show that cos^4 x -sin^4 x = cos2x Im not sure how, I can solve my problem with half angle identities but im not sure where to start with this.

More Similar Questions