This is a common feeling in high school. This happens because you don't fully understand the meaning of the question, and you don't really understand it.

Because in your understanding, what you do is right, but often the topic is not that simple, in fact, there is another meaning. When the score comes out and the teacher explains it, you will think, why didn't I think of it at that time? Actually, I should have thought of it.

Another point is carelessness. Many people actually know how to do it, but carelessness leads to losing points.

For mathematics, you must practice more. Do each question once, and do more simulation questions to improve. In addition, don't disdain to do after-school exercises just because they are simple.

I believe that if you do as I say, you will certainly improve, because that's how my math came from, and I am deeply touched. From more than 90 points to the college entrance examination 128 points, although it is not very high, it has improved.