On this week, we reviewed trigonometry because after winter break, almost classmates may forget the content of trigonometry. This chapter is hardest for me. Basically, we should know new vocabularies to solve the problem. These are standard position, terminal arm , terminal point, reference angle, Sine Law, and Cosine Law. Also we should know the formula ; Sin θ = , Cos θ = , Tan θ = . We can find to be not given side and angle with that formula. When the angle θ, between 0° and 360°, is measured counterclockwise from the positive x-axis, the angle is in standard position. Also we should know about all quadrants. Quadrant 1 : +sin, +cos, +tan. Quadrant 2 : +sin, -cos, -tan. Quadrant 3 : -sin, -cos, +tan. Quadrant 4 : -sin, +cos, -tan. The plus sign and minus sign is important in this chapter. The reference angle for all 4 angles is the acute angle that the terminal arm makes with the x-axis. For example here are all the angles in standard position have a reference angle of 60°. Then in quadrant 1 has 60° in standard position. Quadrant 2 has 120° in standard position. Quadrant 3 has 240° in standard position. Quadrant 4 has 300° in standard position. Also there is a formula that find reference angle to use standard position and find standard position to use reference angle. In quadrant 1 the reference angle is standard position. In quadrant 2 If you want find the reference angle, 180° –   θ = reference angle, and if you want to find the standard position, 180° – reference angle =  θ. In quadrant 3 If you want to find the reference angle,  θ – 180° = reference angle, and if you want to find the standard position, 180° + reference angle = θ . The last in quadrant 4, if you want to find the reference angle, 360° –  θ = reference angle, and if you want to find the standard position, 360° – reference angle = θ. And we also learned about Sine Law and Cosine Law. In these lessons, there are also formula. In Sine Law, = = we use this formula when we want to find missing side. = = we use this formula when we want to find missing angle. In Cosine Law, = + – 2ab Cos A, = + -2ac Cos B, = + -2ab Cos C. We use the Sine Law when we know 2 sides and non included angle, also we use the Sine Law when we know 2 angles and non included side. We use the Cosine Law when we know two sides and the angle between them, and when we know all three sides. If we know basic of this chapter, we can solve all problems.

Thank you