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H2. Solving triangles : find an angle. If two sides of a right-angled triangle are known then you can find the size of any of the angles. Follow these steps. 1. Two sides of a triangle are known. 2. Decide which angle to find and label it q 3. Label the two known sides appropriately as either opposite (o), adjacent (a) or hypotenuse (h). 4. Quote the correct trigonometry formula that uses these two sides. cos q=a/h 5. Substitute in the known values. cos q=7/12 6. Use a calculator to find the value of q. Press INV COS (7÷12) or the equivalent on your calculator. 7. Round off your answer to a suitable accuracy. q=54.3 degrees.