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【题目】求下列各式的值.

1sin 195°+cos 105°;

2cosα-45°cos15°+α+cosα+45°cos105°+α).

【答案】12

【解析】1原式=cos 105°+sin 195°

=cos 105°+sin90°+105°

=cos 105°+cos 105°

=2cos 105°=2cos135°-30°

=2×cos 135°cos 30°+sin 135°sin 30°

=2×

2原式=cosα-45°cos15°+α+sin45°-αcos15°+90°+α

=cosα-45°cos15°+α-sin45°-αsin15°+α

=cosα-45°cos15°+α+sinα-45°sin15°+α

=cos[α-45°15°+α]

=cos-60°=cos 60°=.

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