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FINDING AN UNKNOWN SIDE REMEMBER: Pythagoras’ Theorem is used to find an unknown side in a right angled triangle when the other two sides are known. Trigonometry is used when only one side and one of the acute angles is known. TYPE 1: Unknown Side as the numerator in the trig equation.(MULTIPLY) 1) Find x in these triangles correct to 2 decimal places. b) a) 7.6 m x x 59 31 5m 2) A flagpole has a guy rope from the top of the pole to a point on the ground 12 m from the base of the pole. If the rope makes an angle of 36 with the ground, find the height of the pole. When the unknown side is the numerator in the equation we multiply the number by tan TYPE 2: Unknown side as the denominator in the equation. (DIVIDE) b) a) 49 4m d 25 x 8.6 m c) A ship out at sea observes a lighthouse on the top of a 70 m cliff at an angle of 3. How far out at sea is the ship (to the nearest metre)? 70 m 3 When the unknown is on the bottom of the fraction in the equation we divide the number by tan REMEMBER: Unknown on the TOP of the fraction , MULTIPLY the number by tan Unknown on the BOTTOM of the fraction, DIVIDE the number by tan