Sine, cosine and tangent are the principle trigonometric functions. ... For a right triangle, the side opposite to the right angle is called the hypotenuse (from Greek for “stretching under”).

For two right-angled triangles, if an angle (other than the right angle) is the same, the third angle will also be the same. This is true because angles in a triangle add up to 180°.

Sin, cos and tan are commonly used abbreviations for the three trigonometric functions sine, cosine and tangent. Back to top How to calculate an unknown angle in a right-angled triangle ...