2tana+3sinb=7
4tana+6sinb=14
tana-6sinb=1
相加得
5tana=15
tana=3,cosa=(1/3)sina
因为a是锐角,所以sina>0
sin²a+cos²a=1
sin²a+[(1/3)sina]²=1
10sin²a/9=1
sina=3(根号10)/10