# trigonometry !! a very tricky trick

• Sep 7th 2013, 11:42 AM
SHEvA9
trigonometry !! a very tricky trick
hey there

regarding this problem

i know that i can use the cosine law and then the sine law to investigate whether the other ange must be 45 or not,,
but it takes alot of time and i kinda don't have that much time to solve a problem!!

i don't know if am overlooking other way of doing it??
• Sep 7th 2013, 12:30 PM
Shakarri
Re: trigonometry !! a very tricky trick
I assume you are trying to show if this is true or false. You will have to use the cosine rule then the sine rule but to save yourself a bit of work think about whether the angle $\frac{\pi}{4}$ will be opposite the side with length 4 or 8.
• Sep 7th 2013, 01:20 PM
emakarov
Re: trigonometry !! a very tricky trick
You can solve this without the law of cosines if you note that 180 - 60 - 45 = 75 and 75 - 30 = 45.
• Sep 7th 2013, 03:47 PM
SHEvA9
Re: trigonometry !! a very tricky trick
emakarov,, i didn't really get how could that help me,,

may you please eleborate on that??
• Sep 7th 2013, 10:01 PM
emakarov
Re: trigonometry !! a very tricky trick
Let angle A be 60, AB = 4 and AC = 8. If angle C is 45, then angle B is 75. Draw the altitude BH. Then angle CBH is 45, i.e., BH = HC. Can you finish?
• Sep 20th 2013, 06:40 PM
votan
Re: trigonometry !! a very tricky trick
I understand the problem like this:

one side = 4