Graphing Inequalities and System:
After learning about these graphs separately, I notice that these two can be combined to make a system with two inequalities. By graphing, you can quickly tell the solutions by looking at the graph.
Ex: 
We can graph out this system on the xy-plane:
The overlaping part indicates the solutions for this system.
Sine and Cosine Law:
Before learning about Sine Law and Cosine Law, we can only do the calculation based on the relationship between side lengths and angle of a right triangle. With this two Laws in hand, we are no longer limited; the Sine Law and the Cosine Law enable us to deal with all triangles, given the necessary information.
Special Triangles:
There are some common angles that are used fairly often in trigonometry: 0, 30, 45, 60, 90. By knowing the exact value of sine, cosine, tangent for these angles, it will save you lots of time. But how to remember these values? There is a way: using right isosceles triangle and 30-60-90 triangle.
*Right isosceles triangle:
Base on the triangle and the ratios between the side lengths, we have:
*30-60-90 triangle:
Similarly, we have:
The CAST Rule:
At first, it’s hard to tell which quadrant the terminal arm lies in given a sine/ cosine/ tangent value. However, with the help of this simple rule, we can identify which quadrant that is with ease.
Personal Development:
Last but not least, I am now able to express a math problem and explain it, which I couldn’t in the past. I use more mathematical terms, be capable of putting my solving steps into words for others to understand. Besides, by helping my friends, I get to understand a lesson deeper and remember it over a longer period of time.