If you draw a right-angled triangle, you can find the angles of the triangle by measuring the lengths of the triangle sides. There are three formulae that help you do this. They're called the trigonometric ratios, and they are as follows:

sin theta = length of opposite divided by length of hypotenuse

cos theta = length of adjacent divided by length of hypotenuse

tan theta = length of opposite divided by length of adjacent

To solve a problem involving trigonometry you need to choose the correct trigonometric ratio. In the question, you know the following:

length of hypotenuse = 12

angle between hypotenuse and adjacent = 36°

You want to know the length of the opposite. You need to use the ratio which involves the opposite and hypotenuse, or the sine ratio:

sin 36° = opposite divided by 12

opposite = 12sin 36°

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