Homework Questions Section 3.1Reference Angles The reference angle of any angle in standard position is the acute angle between its terminal side and the xaxis. θ = 95o θ = 340o θ = 200o θ = 55o Why do we care about reference angles? Use your calculator to find each of the following: sin 30o sin 150o sin 210o sin 330o What is the value of the reference angle for each of the angles? What conclusion can we make? θ = 355o θ = 15o You are supposed to have some values memorized... sin 30o cos 30o sin 45o cos 45o sin 60o cos 60o They come up so often that you should know them! How will we use reference angles? To calculate the value of sinθ, cosθ, tanθ, cscθ, secθ, or cotθ... (1) Note the quadrant of the original angle θ and the SIGN of the trig function there! (2) Calculate the value of the reference angle (3) Find the trig function value using the reference angle, then adjust the sign. EXAMPLES: Find the EXACT value of cos 135o Find the exact value of sin 240o. Find the exact value of tan 150o. NOW we can use the reference angle to help us find solutions to trig equations. Find θ if sinθ = θ is in QIV and 0o < θ < 360o Find θ if cosθ = 0.9455 θ is in QIII and 0o < θ < 360o
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