Two sides of a triangle are 10 cm and 8 cm long and the sine of the angle between them is 0.5. What is the area?

1. The area rule works in any triangle and needs no perpendicular height. 2. It gives half the product of two side lengths multiplied by the sine of the angle between them. 3. Multiply the two sides: 10 cm times 8 cm is 80 square centimetres. 4. Multiply by the sine of the included angle: 80 times 0.5 is 40 square centimetres. 5. Take half of that: half of 40 is 20 square centimetres. 6. The area of the triangle is therefore 20 square centimetres. 7. Answering 80 square centimetres uses neither the sine value nor the halving. 8. Answering 40 square centimetres forgets the halving, and 18 square centimetres adds the sides instead. _Source: Siyavula Mathematics Grade 11 (Everything Maths, CC BY 4.0), Chapter 6: Trigonometry_