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1994年高考第18题:已知sinθ+cosθ=1/5,θ∈(0,π).则ctgθ的值是_____.部分同学的答案是-3/4或-4/3.而正确的答案是-3/4.造成错误的原因是忽略了sinθ+cosθ=1/5中隐含的角的范围.在教学中如何挖掘角的隐含范围呢?我认为需要从以下五方面入手.
The 1994 college entrance examination question 18: known sin θ + cos θ = 1/5, θ ∈ (0, π). Then the value of ctg θ is _____. Some students’ answers are -3/4 or -4/3. The answer is -3/4. The reason for the error is to ignore the range of angles implicit in sinθ+cosθ=1/5. How do you mine the implicit range of angles in teaching? I think we need to start from the following five aspects. .