## boomerang285 one year ago Please help... Determine the measure of side c, given: a=3m b=4m B=41deg

1. AravindG

tried cosine rule ?

2. boomerang285

im not sure how to do this at all....

3. AravindG

do u knw cosine rule ?

4. boomerang285

i have just started learning about it

5. AravindG

ok $\cos B=\dfrac{a^2+c^2-b^2}{2ac}$

6. AravindG

now solve for b

7. t_soulb

yea good cosine rule,,my answer is b=2.44 (approx.)

8. dan815

u could use sin law too i think

9. t_soulb

sorry 1.22

10. AravindG

@dan815 sin law wont work cause we need two angles :/

11. dan815

sin <b/b=sin<a=a sin<(180-(a+b))/c and solve for C

12. dan815

use my equation < means angle

13. boomerang285

actually my options are: 1.6m 4.5m 0.1m 5.7m I thought it was 1.6m?

14. boomerang285

am I wrong?

15. boomerang285

actually it was 5.7 after I figured it out.. Thanks though

16. dan815

did u use my formula!

17. t_soulb

yea approx.

18. boomerang285

yes thank you

19. dan815

np :)

20. dan815

if u remember that you need atleast 3 pieces of information to solve a triangle and that if the angle given is the angle of the opposite side then you can always use sin law if they give u like side a and b but give you angle C then you have to use cos law if its not a right angle triangle