I didn't learn trigonometric functions in school. How can I calculate this using PHP?

Just use PHP to find the position of point c on the y-axis, thank you..

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Just use PHP to find the position of point c on the y-axis, thank you..

This does not require trigonometric functions, similar triangles; for example, the coordinates of B are (5, 2.5). The abscissa of c is 12, then the y coordinate of c is 5/12=2.5/cy, and the y coordinate of c can be obtained 6

Answer: 6.
Triangles are similar, you can get it by comparing them. As for how to calculate it in PHP, you can write it yourself.