sin^2 15°-cos^2 15°的值是A.-√3/2 B.1/2 C.-1/4 D.3/4
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sin^215°-cos^215°的值是A.-√3/2B.1/2C.-1/4D.3/4sin^215°-cos^215°的值是A.-√3/2B.1/2C.-1/4D.3/4sin^215°-cos^2
sin^2 15°-cos^2 15°的值是A.-√3/2 B.1/2 C.-1/4 D.3/4
sin^2 15°-cos^2 15°的值是
A.-√3/2 B.1/2 C.-1/4 D.3/4
sin^2 15°-cos^2 15°的值是A.-√3/2 B.1/2 C.-1/4 D.3/4
原式=-(cos^2 15°-sin^2 15°)
=-cos30度
=-√3/2
选A
=-cos30°
=-√3/2
A
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