
Teaching Trigonometry Cosine Functions  Fun Math Help  Game Tips:  Press the 't' key to see a graph that demonstrates the following example. The cosine of angle A can be written as cos A and cos A equals the ratio (x/r) = (3)/(5) when point D is (x,y) = (3,4) and r=AD=5. With angle A in standard position at the origin, the cosine ratio of A is (x coordinate)/(radius) = (3)/(5). The radius r=5 can be calculated from point D(3,4) using 3^{2} + 4^{2} = r^{2}.  Press the 'y' key to restart the game.  When angle A is in standard position at the graph's origin (0,0) then cos A equals (x/r). Since r is the hypotenuse of a right triangle, r can be found from point D(x,y) using x^{2} + y^{2} = r^{2} . Consequently, cos A can also be described as (adjacent side)/(hypotenuse).  The small square symbol at B indicates AB is perpendicular to BD forming a right angle.  It may take a minute to load the game at dialup speeds.  The game can be played using the mouse by itself or using the keyboard by itself.  If the game doesn't respond to keyboard input, click inside the game area to reset the game's focus.  Adjust the game's speed by pressing the + or  key repeatedly. 
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