# 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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