admin百科知識 2022-02-13 18:49:13 已知sin(a+π4)=13,a∈(π2,π)則sin2a=已知sin(a π/4)=1/3,a∈(π/2,π)則sin2a=網友廻答:匿名網友由sin(a π/4)=1/3,a∈(π/2,π)即在第二象限,sinacosπ/4 cosasinπ/4=1/3(√2/2)sina (√2/2)cosa=1/3兩邊平方得:(1/2)sin²a sinacosa (1/2)cos²a=1/9,sinacosa=1/9-1/2(∵sin²a cos... db標簽 生活常識_百科知識_各類知識大全»已知sin(a+π4)=13,a∈(π2,π)則sin2a=
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