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Sinθ+Cosθ=√2,(Sinθ+Cosθ)²=2,Sin²θ+Cos²θ+2SinθCosθ=2,SinθCosθ=1/2;
(Sin²θ+Cos²θ)/SinθCosθ=2,tanθ + 1/tanθ =2,tan²θ - 2tanθ+ 1=0,（tanθ-1）²=0
tanθ=1