问题
填空题
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答案
+4cos70°=1 tan70°
+4cos70°=cos70° sin70° cos70°+4sin70°cos70° sin70°
=
=cos70°+2sin140° sin70°
=cos70°+2sin40° sin70° cos70°+2sin(70°-30°) sin70°
=cos70°+2sin70°cos30°-2cos70°•sin30° sin70°
=2sin70°•cos30° sin70°
=2cos30°=
．3
故答案为：3