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Mathematics 7 Online
OpenStudy (kittiwitti1):

Trig question: needs checking. Diagrams and calculations below

OpenStudy (kittiwitti1):

|dw:1430116667393:dw|

OpenStudy (tylerd):

length from a to b is 37.66km? and length from b to c is 2km?

OpenStudy (kittiwitti1):

What I did (all trig functions are in degrees):\[b^{2}=a^{2}+c^{2}-2ac\cos B\]\[=2^{2}+37.66^{2}-2(2)(37.66)\cos 132\]\[\approx1321.48\]

OpenStudy (kittiwitti1):

@TylerD Yes

OpenStudy (tylerd):

have you tried law of sines?

OpenStudy (kittiwitti1):

I used the Cosines Law. I'm wondering if I did it right...

OpenStudy (tylerd):

looks right

OpenStudy (tylerd):

but did u take the square root after

OpenStudy (tylerd):

im getting 39.0265km for b

OpenStudy (tylerd):

wait a sec

OpenStudy (kittiwitti1):

Okay thanks. Since they want angle A, can I use the value of "segment b" that I found to do the Sine Law? :o (I lagged out sorry) yeah sorry I forgot to square root, you're right... But I got 36.35km.

OpenStudy (tylerd):

now that you have an angle and the side, you can use sine law but

OpenStudy (kittiwitti1):

I calculated sqrt and got 36.___ both ways o_o; did I do something wrong

OpenStudy (tylerd):

2^2+37.66^2=1422.2756 1422.2756-(2*2*37.66cos(132)) = 1523.073435 sqrt(1523.073435)=39.02657344

OpenStudy (kittiwitti1):

O_O I didn't get that at all...

OpenStudy (kittiwitti1):

I re-calculated and got 1550.0256

OpenStudy (tylerd):

sin(132)/39.03 = sin(A)/2 2(sin(132))/39.03=sin(A) sin^-1(2(sin(132))/39.03)=A

OpenStudy (kittiwitti1):

OH I did addition on accident! *facepalms*

OpenStudy (kittiwitti1):

Okay, so I got 1523.07 which square roots to 39.02...

OpenStudy (tylerd):

right now use law of sines.

OpenStudy (kittiwitti1):

and then I should be good for angle A?

OpenStudy (tylerd):

and then solve for theta with a sin inverse

OpenStudy (tylerd):

ya

OpenStudy (kittiwitti1):

Okay

OpenStudy (kittiwitti1):

Thank you ! :)

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