救命啊,(2cos10°-sin20°)÷sin70°

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救命啊,(2cos10°-sin20°)÷sin70°救命啊,(2cos10°-sin20°)÷sin70°救命啊,(2cos10°-sin20°)÷sin70°原式=(2cos10°-sin20°)

救命啊,(2cos10°-sin20°)÷sin70°
救命啊,(2cos10°-sin20°)÷sin70°

救命啊,(2cos10°-sin20°)÷sin70°
原式= (2cos10°-sin20°)/sin70°
=(2cos10°-sin20°)/cos20°
=[cos10°+(cos10°-cos70°)]/cos20°
=[cos10°+2sin40°*sin30°]/cos20°
=[cos10°+2*1/2*sin40°]/cos20°
=[cos10°+cos50°]/cos20 °
=2cos30°*cos20°/cos20°
=2cos30°
= 根号3