求值,三角函数

(sin(15-8)+cos15sin8)/(cos(15-8)-sin15sin8)
=(sin15cos8)/(cos15cos8)
=tan15

(sin7+cos15sin8)/(cos7-sin15sin8)
====积化和差
=[sin7+(sin23-sin7)*0.5]/[cos7+(cos23-cos7)*0.5]
=(0.5sin7+0.5cos23)/(0.5cos7+0.5cos23)
====约分,和差化积
=(sin15*sin8)/(cos15*cos8)
====约分
=tan15(即tg15,我不知道你习惯用那种方式表示 正切)
====半角公式
=(1-cos30)/sin30
=2-3^(1/2) 就是2-根号3

参考:

(sin7+cos15sin8)/(cos7-sin15sin8)
=[sin7+cos(7+8)sin8]/[cos7-sin(7+8)sin8]
=[sin7+(cos7cos8-sin7sin8)sin8]/[cos7-(sin7cos8+sin8cos7)sin8]
=(sin7+cos7cos8sin8-sin7sin²8)/(cos7-sin7sin8cos8-sin²8cos7)
=(sin7-sin7sin²8+cos7cos8sin8)/(cos7-sin²8cos7-sin7sin8cos8)
=[sin7(1-sin²8)+cos7cos8sin8]/[cos7(1-sin²8)-sin7sin8cos8]
=(sin7cos²8+cos7cos8sin8)/(cos7cos²8-sin7sin8cos8)
=(sin7cos8+cos7sin8)/(cos7cos8-sin7sin8) {每项除以cos8}
=sin(7+8)/cos(7+8)
=sin15/cos15
=tan15