=sin 60.sin10.sin50.sin70
= [(√3)/2]sin10sin50sin70
= [(√3)/2]sin10(cos(-20) - cos120)/2
= [(√3)/2]sin10(cos20 - cos120)/2
= [(√3)/2](sin10cos20 - sin10cos120)/2
= [(√3)/2](sin30 + sin(-10) - 2sin10cos120)/4
= [(√3)/2](sin30 + sin(-10) + sin10)/4
= [(√3)/2](1/2)/4
= (√3)/16