第30题: [单项选择]下列哪个选项是正确计算角度42°的余弦值( ) A. double d = Math. cos(42); B. double d = Math. cosine(42); C. double d = Math. cos(Math. toRadians(42)); D. double d = Math. cos(Math. toDegrees(42)); 参考答案:C 答案解析:[解析] public static double cos(double a)是Math类中返回以弧度为单位的a的余弦值的,应先用toRadians()方法将42°转换为弧度值。