PreCal
posted by Adrianna on .
Two airplanes take off from an airport at the same time. One travels on a heading of 45 at 420 mph and the other on a heading of 150 at 400 mph. After two hours, how far apart are the airplanes?
A.650.66 miles
B.1,160 miles
C.1,301 miles

Use the cosine law, I got 650.66

Can you tell me how you did it? I got 5 more questions like this one.

are you not familar with the cosine law?
You must have learned this to be able to do this kind of question. 
Yes I am, but I don't understand it. I don't have a teacher to teach me. I do my work online, and I just need 2nd semester of precal to graduate.

x^2 = 420^2 + 400^2  2(420)(400)cos 105°
do the arithmetic
I got 105° from the difference between 150° and 45° 
thanks

d1 = 420mi/h[45o] * 2h = 840mi[45o]
d2 = 400mi/h[150o] * 2h = 800mi[150o]
D = 840[45o]  800[150o]
X = 840*Cos45  800*cos150 = 1287 mi
Y = 840*sin45  800*sin150 = 194 mi
D = sqrt(1287^2+194^2) = 1301.5 mi