Question

第2题怎么计算？

请好心的数学学霸告诉我，十万火急

Answer 1

都对。

两人都对

Answer 2

都对，一个是按正弦算的，一个是按余弦算的。正弦等于对边比斜边。余弦等于邻边比斜边。三角形180°的内角和，一个90°，一个28°，剩下不就是62°。

Answer 3

Both students' equations are right. Because that sine of an angle is the lengths ration of opposite side to hypotenuse, cosine is that of adjacent side to hypotenuse.
The angle HGJ is 28 degree, whose opposite side is HJ, and hypotenuse HG is 20. So
sin 28 degree is HJ/20.
The angle GHJ, the residual of the angle HGJ, is 90-28=62 degree. So
cos 62 degree is HJ/20.