1, and the range refers to the frequency range of triangular wave. For example, the frequency of input triangular wave is fixed and the range of change is zero. Little change means that the frequency of triangular wave changes around a certain frequency. In this way, a low-pass filter can be designed with reference to this frequency, so that the fundamental signal is basically not attenuated, while the harmonics above the third order are greatly attenuated, and an approximate sine wave can be obtained.

2. The broken line method refers to segmenting the edges of the triangular wave, changing the slope of each segment, and making the triangular wave approximately "folded" into a sine wave. But this method should be used to generate approximate sine waves, rather than input triangular waves and output sine waves. The latter is difficult to achieve and has no practical significance. The former is just a concept, and the actual triangular wave can be generated by sine look-up table method, and the output is more accurate.

3. The signal composition from triangle wave to sine wave can be analyzed. This method is generally not used to actually generate sine waves. Because there are many ways to generate sine waves directly, which is convenient and accurate.