cos15度(cos15度+sin15度)

（sin7度+cos15度sin8度）/（cos7度+sin15?

=[sin(15-8)+cos15sin8]/[cos(15-8)-sin15sin8]

=[(sin15cos8-cos15sin8)+cos15sin8]/[(cos15cos8+sin15sin8)-sin15sin8]

=sin15cos8/(cos15cos8)

=tan15

=(1-cos30)/sin30

=(1-√3/2)/(1/2)

=2-√3.

怎麽設計cos15度和cos22.5度

cos15=cos(45-30)=cos45cos30+sin45sin30=√2/2*√3/2+√2/2*1/2=(√6+√2)/4cos45=√2/2=2cos222.5-1cos222.5=(√2+2)/4cos22.5>0cos22.5=√(√2+2)/2

本文到此結束，希望對大家有所幫助呢。