half-angle of projection

例句：

1. 1.The projector's half-angle is crucial for the image quality.
   投影机的半角对图像质量至关重要。
2. 2.The scientist used a half-angle to measure the angle of the sun.
   科学家用一个半角来测量太阳的角度。
3. 3. The engineer calculated the half-angle of the triangle using the Pythagorean theorem.
   工程师使用勾股定理计算了这个三角形的半角。