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Definitions:
Centroid of a triangle - center (where the lines bisecting each angle will meet)
Area of a triangle = base*height/2
Heron's formula - area of any triangle, with sides of length a, b, c, don't know height:
Theorems to prove triangles are congruent:
* 45-45-90 triangle: hyp = side * √2 * 30-60-90 triangle: short side = a, long side = a*√3, hyp = 2a * 3-4-5 triangle: if a triangle has sides 3n and 4n, then the hypotenuse will be 5n
area of a right triangle = 1/2*h*w
hypotenuse is the side opposite the right angle, opposite is the side opposite the given angle, adjacent is the side next to the given angle
SOHCAHTOA (pronounced "Soak a toe-ah"): Sin=Opp/Hyp, Cos=Adj/Hyp, Tan=Opp/Adj
law of sines:
sin(A)/a = sin(B)/b = sin(C)/c (sometimes a/sin(A) = ...)
law of cosines - to find an angle when all the sides are known
cos(A) = (b² + c² - a²) / (2bc) cos(C) = (a² + b² - c²) / (2ab), cos(B) is same pattern (side a is opposite angle A, etc) rewriting it: c = √(a² + b² - 2abcos(C))