



 
Hi Kobina. Let's draw a right angled triangle showing the northsouth direction and the eastwest direction. As you can see, the lengths of the lines indicate the speeds. Can you see how the length of the bottom line represents the speed the airplane travels westward? How long that line is depends on the angle and the length of the hypotenuse. We can use the Cosine function (COS) to find the length of a leg of a rightangled triangle when we know the length of the hypotenuse and the angle between them. Cosine = adjacent / hypotenuse So in your case, the hypotenuse length is the speed of the actual airplane (500mph) and the angle is 40 degrees. Let's let the length of the unknown eastwest line be x mph. We have:
The answer is 383 mph. We call this the component of the speed of the airplane that is moving westwards. Hope this helps,  


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences. 