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H2. Solving triangles : find a side. If the angles in a right-angled triangle and one of the sides are known, then you can find the length of either of the other sides. Follow these steps. 1. A side and an angle of a triangle are known. 2. Decide which other side to find and label it x 3. Label the two sides appropriately as either opposite (o), adjacent (a) or hypotenuse (h). 4. Quote the correct trigonometry formula that uses these two sides. sin q=o/h 5. Substitute in the known values. sin 60=x/12 6. Use a calculator to find the value of x. Press 12 × SIN 60 or the equivalent on your calculator. 7. Round off your answer to a suitable accuracy. x=10.4 cm.