Review from yesterday…

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Presentation transcript:

Review from yesterday… Solve ΔSJT given s = 49, side j = 16, and angle S = 115°. S = _____ J = _____ T = _____ s = _____ j = _____ t = _____

Answer Solve ΔSJT given s = 49, side j = 16, and angle S = 115°. S = 115° J = 17.21° T = 47.79° s = 49 j = 16 t = 40.05

Law of Cosines

Remember how we need buddies to use the Law of Sines? In order to use the Law of Sines, we need a side and its corresponding angle to apply to the ratio. What if we don’t have buddies?

Law of Cosines! Let ΔABC be any triangle with angles A, B, and C opposite sides a, b, and c, respectively, then following equations are true: a2 = b2 + c2 – 2bc cos A b2 = a2 + c2 – 2ac cos B c2 = a2 + b2 – 2ab cos C We decide which equation to use by using the angle we have (or the angle we want to find!).

Example 1: No buddies, no problem! Solve ΔABC given that a = 11, b = 5, and angle C = 20°. A = _____ B = _____ C = _____ a = _____ b = _____ c = _____

Example 2: You try! Solve ΔABC if a = 9, b = 7, and c = 5. A = _____ B = _____ C = _____ a = _____ b = _____ c = _____