问题
选择题
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答案
sin47°-sin17°cos30° cos17°
=sin(17°+30°)-sin17°cos30° cos17°
=sin17°cos30°+cos17°sin30°-sin17°cos30° cos17°
=sin30°=
．1 2
故选C
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sin47°-sin17°cos30° cos17°
=sin(17°+30°)-sin17°cos30° cos17°
=sin17°cos30°+cos17°sin30°-sin17°cos30° cos17°
=sin30°=
．1 2
故选C