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在计算或化简三角函数关系式时 ,常需对角的范围以及相应三角函数值的符号情况进行讨论 ,若审题不细不严 ,很容易出错 .故解答这类问题时 ,要三思而后行 ,形成审慎思维的习惯 .一、不注意挖掘题设条件 ,扩大了角的取值范围例 1 已知sinA -sinB =-23 ,①cosA-cosB =23 ,②且A、
When calculating or simplifying the trigonometric function relations, it is often necessary to discuss the range of the diagonal angle and the sign of the corresponding trigonometric function value. If the question is not strict, it is easy to make mistakes. Therefore, when answering such questions, think twice before proceeding. , Forming a habit of prudent thinking. First, pay attention to digging questions to set the conditions and expand the scope of the angle. Example 1 Known sinA - sinB = -23, 1cosA-cosB = 23, 2 and A,