## anonymous one year ago help please

1. anonymous

With?

2. anonymous

3. campbell_st

well you can use the law of cosines to check do you know how to use it..?

4. anonymous

no i dont :(

5. jennyrlz

sec let me see what i can remeber :)

6. anonymous

k

7. anonymous
8. anonymous

im to lazy to draw the abc triangle lol, but that explains the law of cosines well

9. campbell_st

the law of cosines says $Cos(A) = \frac{b^2 = c^2 - a^2}{2bc}$ does that help

10. campbell_st

you have a = 5.3, b = 7 and c = 4... plug them in and post the answer you get

11. campbell_st

oops should read $\cos(A) = \frac{b^2 + c^2 - a^2}{2bc}$

12. jennyrlz

^

13. anonymous

oh wait is it true?

14. jennyrlz

ill leave it to him, he knows what he is doing :)

15. jennyrlz

oh he left...

16. jennyrlz

well why do you think it is true?

17. jennyrlz

he did the "hard" part the rest is algebra

18. campbell_st

well you need to find the angle measure using the law of cosines to see if its true or not

19. campbell_st

an alternative solution is to google a triangle solver put in the 3 sides and then look at the angles that are calculated

20. anonymous

which law of cosine should i use

21. jennyrlz

if only i wouldve thought of this when i was taking pre-calc...

22. campbell_st

use the one I posted above

23. anonymous

how do i use it....do i sub

24. campbell_st

and look for the measures that match the labels a, b and c

25. campbell_st

a = 5.3 b = 7 and c = 4 like this $cos(\theta) = \frac{7^2 + 4^2 - 5.3^2}{2 \times 7 \times 4}$

26. anonymous

doin the math.....

27. anonymous

$\cos \theta \frac{ 49+16-28.09 }{66 }$ thats what i have so far

28. anonymous

is it right

29. anonymous

so far

30. campbell_st

well I think the denominator is 56

31. campbell_st

2 x 4 x 7 = 56

32. anonymous

oh yea

33. anonymous

wait so it is true?

34. campbell_st

not yet, if you do the calculation you'll find $\cos(\theta) = 0.659107$ so to find the angle, using a calculator its $\theta = \cos^{-1}(0.659107)$

35. anonymous

i got 0.79053943 ? how do i punch this equation in a calculator