Use it when you know the length of the hypotenuse and the adjacent side.
Cosine
What is the equation for Sine Rule
What is one of the three equations for cosines?
cos(C) = a2 + b2 − c2 2ab.
cos(A) = b2 + c2 − a2 2bc.
cos(B) = c2 + a2 − b2 2ca.
[[2,5],[-2,8]]+[[1,4],[5,0]]
[[3,9],[3,8]]
[[2,3],[1,x]]+[[4,3],[6,6]]=[[6,6],[7,11]]
x=5
Use it when you know want to know the opposite side and you know the measure of the angle and adjacent side.
Tangent
What angle should be found first if given sides a and b and angle A?
Angle B
What is the cosine of 90o?
0
[[8,16,-3],[2,20,10]]-[[5,11,7],[-3,6,6]]
[[3,5,-10],[5,14,4]]
[[6,3,x],[5,9,2]]+[[4,1,11],[-4,9,6]]=[[10,4,22],[1,18,8]]
x = 11
cos 0 degrees?
1
What type of triangle is the Law of Sines used for?
Non-right triangles
What Theorem does this equation resemble?
Pythagorean theorem
5[[4,5,1],[0,-2,7]]
[[20,25,5],[0,-10,35]]
[[8,10,-3],[2,2,1]]-[[7,2,1],[x,6,4]]=[[1,8,-4],[6,-4,-3]]
x = -4
Solve:
Cos 40 = x/12
9.2
When would you use the law of sines?
When you have AAS or SSA in a triangle
When would you use the Law of Cosines?
When a triangle has either SSS or SAS
[[6,2],[-1,5]]*[[2],[1]]
[[14],[3]]
2[[1,6,5]]+[[4,x,1]]=[[6,15,11]]
x = 3
Solve:
Tan x = 3/2
56.3
When given b= 2, A= 45o, and B= 30o, What does a equal?
a = 2.8
When would you use the cosine inverse?
When you need to find the angle
[[3,1],[2,2]]*[[4,1],[2,1]]
[[14,4],[12,4]]
5[[-3,1,6],[4,1,1]]+2[[5,11,2],[2,9,x]]-4[[1,0,2],[4,1,1]]=[[-9,27,26],[8,19,17]]
x = 8