By David Cho

 Trigonometry is a branch of mathematics deali ng with angles, triangles, and trigonometric fun ctions such as sine, cosine, and tangent.  SOH, CAH, TOA  c 2 = a 2 +b 2  Sine Law  Cosine Law

 The coordinates of a point P on the coordinate plane can be described by its distance r from the origin O, and the angle θ that OP makes with the positive x-axis. When the a ngle θ (between 0º and 360º) is measured counterclockwi se from the positive x-axis, the angle is in standard positio n. The ray OP is the terminal arm of the angle and the poin t P is terminal point for the angle.

 The Reference Angle of all 4 angles (90°, 180°, 270°, and 360°) is the acute angle that the terminal arm makes with the x-axis.

 For any angle θ in standard position, where 0º =< θ =< 360º, with terminal point P(x, y), the primary trigonometric ratios are:  Cos θ = x/r r = √(x 2 +y 2 )  Sin θ = y/r  Tan θ = y/x

 Quadrant 1 cos θ = x/r Positive (x, y) sin θ = y/r Positive tan θ = y/x Positive  Quadrant 2 cos θ = x/r Negative (-x, y) sin θ = y/r Positive tan θ = y/x Negative

 Quadrant 3 cos θ = x/r Negative (-x, -y) sin θ = y/r Negative tan θ = y/x Positive  Quadrant 4 cos θ = x/r Positive (x, -y) sin θ = y/r Negative tan θ = y/x Negative

 Sine Law  Cosine Law

 c = a/sin A = b/sin B = c/sin C - Sine Law

 618&espv=2&biw=1366&bih=667&source=lnms&tbm=isch&sa=X&ved=0 ahUKEwirqfX6rrzKAhVFy2MKHY6pBpwQ_AUIBigB#tbm=isch&q=right+triang le+xy+&imgrc=_  618&espv=2&biw=1366&bih=667&s=_  plane-so html    &espv=2&biw=1366&bih=667&source=lnms&tbm=isch&sa=X&ved=0ahU KEwjSmJ6Ds7zKAhUT8WMKHdldCsMQ_AUIBigB#imgrc=561zH79rruaEPM %3A

  &espv=2&biw=1366&bih=667&source=lnms&tbm=isch&sa=X&ved=0ahU KEwjSmJ6Ds7zKAhUT8WMKHdldCsMQ_AUIBigB#tbm=isch&q=cosine+law &imgrc=VzX3jM_n7iuAdM%3A  asp  617CA618&espv=2&biw=1366&bih=667&s=_  the-xy-plane-so html