α=30 x=3.88 см n=1.5 h=?
sin(α-β)=x/L h=x*cos β/(sin(α-β)
sin(α-β)=sin α*cosβ - cos α*sinβ
sin α/sin β=n
h=x/(sin α*(1-cos α/(√(n² - sin²α)))=3.88/(0.5*(1-0.866/√(1.5²-0.5²)))=20.4 см
