Help with Mrs.Hale

Help with Mrs.Hale

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  • In order to solve Law of Sine's and Cosine problems, you need to know their formulas and you will be okay 
  • Okay, I remember that the Law of Sines formula was  SinA/a= SinB/b= SinC/c
  • Okay.
  • Correct, so lets start with a problem for this law since you remember the formula. 
  • Yes, Awesome work! Now cross multiply.
  • A
  • First, you have to create your equation using the formula 
  • c
  • Sin53/c = Sin38/6
  • 38
  • B
  • 53
  • 6
  • C
  • Sin(53)*6=Sin(38)c
  • Sin(53)*6/Sin38)
  • Side c=7.8
  • Plug it into your claculator
  • Now get c by itself
  • Great work! Now let's move onto Law of Cosine. 
  • The formula for law of cosine to find a is a^2=(b^2)+(c^2)-2(a)(b)cosA.
  • So we plug in the numbers into the formula which corresponds with the angle we are tyring to find
  • Correct, and those variable can be changed depending on the side or angle you have to find
  • So let's try to figure out the angle of B
  • A
  • 8
  • 35
  • B
  • 5
  • 108.9
  • 4.8
  • C
  • Correct, so in this case, we would use the formula 5=(4.8^2)+(8^2)-2(4.8)(8)cosB
  • Then we combine like terms to get 25=87.04-78cosB. Subtract 87.04 on both sides to get -62.04=-76.8cosB
  • Correct. Now we have to get cosB by itself so we have to divide by -76.8 on both sides to get cosB=-62.04/-76.8.
  • Then we have to find the inverse of cosine, right?
  • Yes
  • So that would be B=cos^-1=-62.04/-76.8. And we plug that into the calculator to get the angle of measure B as 36.1 degrees
  • Correct! See you got the hang of this. Just practice any more problems and you will be fine. 
  • B=36.1
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