websaler
幼苗
共回答了10个问题采纳率:100% 举报
1.(sin7+cos15sin8)/(cos7-sin15sin8)
=[sin7+(sin23-sin7)*0.5]/[cos7+(cos23-cos7)*0.5]
=(0.5sin7+0.5cos23)/(0.5cos7+0.5cos23)
=(sin15*sin8)/(cos15*cos8)
=tan15
=(1-cos30)/sin30
=2-√3
2.(2cos10-sin20)/sin70
=(2cos10-sin(30-10))/sin70
=(2cos10-(sin30cos10-cos30sin10))/sin70
=(2cos10-1/2cos10+√3/2sin10)/sin70
=(3/2sin10+√3/2sin10)/sin70
=√3(√3/2cos10+1/2sin10)/sin70
=√3 sin(10+60)/sin70
=√3
1年前
8