第3个回答 2020-04-21
①sin15度=sin(60度-45度)
=sin60cos45-cos60sin45
=√3/2×√2/2一1/2×√2/2
=(√6-√2)/2
②tan105度=tan(60度+45度)
=(tan60+tan45)/(1-tan60 ×tan45)
=(√3+1)/(1-√3)
=-2-√3
③cos兀/12=cos15度
=cos(45度-30度)
=cos45cos30+sin45sin30
=√2/2×√3/2+√2/2×1/2
=(√6+√2)/4
④sin165度=sin15度
=sin(45度-30度)
=sin45cos30-sin30cos45
=(√6-√2)/4本回答被提问者采纳