# Week 17 in Prec 11

After having the winter break, we came back to school in week 17. In the new week, we learnt the    Trigonometry. The primary trig ratios are “sin”, “cos”, “tan”.

In the any triangles, we can find these three values for each angle, we have learnt the simple in math 10, so the important thing in this unit are Sine Law and Cosine Law.

For the sine law, if we know one angle and its opposite line and a side line, or we know two angles and the opposite line of one of them, we can use the sine Law.

This is the cosine law, in fact, there are three functions for each angle, we can use this one to change into the other two. If we know three line or one angle and its two adjacents, we can use the cosine Law.

And in the end, we have biggest angles in this unit, so the symbol of three ratios will change.

For the quadrant 1, sin, cos and tan are all positive; and the Q2, sin is positive, cos and tan are negative; tan is positive , sin and cos are negative in the Q3; in the end, cos is positive, tan and sin are negative in the Q4. It make a sentence: All students take calculate(ASTC). Easy to remember!

Top1: chapter8, absolute value and reciprocal functions

Top2: chapter6, trigonometry