Tuesday
July 22, 2014

Homework Help: Math question - plz correct

Posted by May on Tuesday, May 27, 2008 at 7:51pm.

Two airplanes leave an airport at the same time. One travels at 355km/h and the other at 450km/h. Two hrs later they are 800km apart. Find the angle between their courses.

a^2 = b^2 + c^2 - 2bc Cos A
800^2= 450^2 + 355^2 - 2(450)(355) Cos A
640000= 202 500 + 126 025 - 319 500 Cos A
640 000-328 525 = -319 500 Cos A
311 475= -319 500 Cos A
311 475/ -319 500= Cos A
-0.9749= Cos A
167.13 = A

Can you please explain to me what is wrong with this? I checked the back of the book and the answer is suppose to be 58.17

thanks~!

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