Question 11857
draw a right-angled triangle... a horizontal line AB and a vertical line BC at the right-end of the horizontal line. The hypotenuse is AC.


Now, draw another vertical line DE where D is some point on line AB...your choice and E is the other end of the line, somewhere on AC. OK so far?


Right, the angle A is whatever angle it is. The "interesting" or at least useful property is that the ratio of the sides in triangles ABC and ADE are the same... so AB/AC is the same as AD/AE etc.


So, we can use this fact that ratios of sides for a given angle are the same. Now there are 3 possible combinations of sides (well 6 actually). These are:


opposite/adjacent
adjacent/opposite


opposite/hypotenuse
hypotenuse/opposite


adjacent/hypotenuse
hypotenuse/adjacent


and these ratios have names:


opposite/adjacent --> tangent
adjacent/opposite --> cotangent


opposite/hypotenuse --> sine
hypotenuse/opposite --> cosecant


adjacent/hypotenuse --> cosine
hypotenuse/adjacent --> secant


For basic trig, you will use SIN, COS and TAN, the 3 "basic" ratios.


jon.