Trigonometric Ratios A RATIO is a comparison of two numbers. For example; boys to girls cats : dogs right : wrong. In Trigonometry, the comparison is between sides of a triangle.

Trig. Ratios Name “say” SineCosinetangent Abbreviation Abbrev. SinCosTan Ratio of an angle measure Sinθ = opposite side hypotenuse cosθ = adjacent side hypotenuse tanθ =opposite side adjacent side

Easy way to remember trig ratios: SOH CAH TOA Three Trigonometric Ratios Sine – abbreviated ‘sin’. –Ratio: sin θ = opposite side hypotenuse Cosine - abbreviated ‘cos’. –Ratio: cos θ = adjacent side hypotenuse Tangent - abbreviated ‘tan’. –Ratio: tan θ = opposite side adjacent side Θ this is the symbol for an unknown angle measure. It’s name is ‘Theta’.

Let’s practice… B c a C b A Write the ratio for sin A Sin A = o = a h c Write the ratio for cos A Cos A = a = b h c Write the ratio for tan A Tan A = o = a a b Let’s switch angles: Find the sin, cos and tan for Angle B: Sin B = b c Cos B = a c Tan B = b a

I want to findUse these calculator keys Ratio of sides as a decimalRegular keys A missing side SIN COS TAN Angle measure SIN -1 COS -1 TAN -1 To set your calculator to DEGREE: MODE (next to 2 nd button) Degree (third line down… highlight it) Enter 2 nd Quit Make sure you have a calculator…

Let’s practice… C 2cm B 3cm A Find an angle that has a tangent (ratio) of 2 3 Round your answer to the nearest degree. Process: I want to find an ANGLE I was given the sides (ratio) Tangent is opp adj TAN -1 (2/3) = 34°

Practice some more… Find tan A: A 21 Tan A = opp/adj = 12/21 Tan A = A Tan A = 8/4 = 2 8 Find tan A:

Trigonometric Ratios When do we use them? –On right triangles that are NOT or Find: tan 45 1 Why? tan = opp adj

Using trig ratios in equations Remember back in 1 st grade when you had to solve: 12 = x What did you do? 6 (6) 72 = x Remember back in 3rd grade when x was in the denominator? 12 = 6 What did you do? x (x) 12x = 6 __ 12 x = 1/2

x cm 15 cm 34° Ask yourself: In relation to the angle, what pieces do I have? Opposite and hypotenuse Ask yourself: What trig ratio uses Opposite and Hypotenuse? SINE Set up the equation and solve: Sin 34 = x 15 (15) (15)Sin 34 = x 8.39 cm = x

x cm 12 cm 53° Ask yourself: In relation to the angle, what pieces do I have? Opposite and adjacent Ask yourself: What trig ratio uses Opposite and adjacent? tangent Set up the equation and solve: Tan 53 = x 12 (12) (12)tan 53 = x cm = x

x cm 18 cm 68° Ask yourself: In relation to the angle, what pieces do I have? Adjacent and hypotenuse Ask yourself: What trig ratio uses adjacent and hypotnuse? cosine Set up the equation and solve: Cos 68 = 18 x (x) (x)Cos 68 = 18 X = 18 cos 68 _____ cos 68 X = cm

42 cm 22 cm θ This time, you’re looking for theta. Ask yourself: In relation to the angle, what pieces do I have? Opposite and hypotenuse Ask yourself: What trig ratio uses opposite and hypotenuse? sine Set up the equation (remember you’re looking for theta): Sin θ = Remember to use the inverse function when you find theta THIS IS IMPORTANT!! Sin = θ °= θ

17 cm 22 cm θ You’re still looking for theta. Ask yourself: What trig ratio uses the parts I was given? tangent Set it up, solve it, tell me what you get. tan θ = THIS IS IMPORTANT!! tan = θ °= θ

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