[math]\Theta = \frac{m_ec^2}{E_{beam}} = \frac{0.511\ MeV}{44\ MeV} = 0.67\ ^o[/math]
[math]\Delta = 286\ cm\ *\ \tan(0.67^o) = 3.34\ cm[/math]
[math]x^2+x^2 = 3.34^2\ cm \ \ \Rightarrow\ \ x = 2.36\ cm[/math]
[math]\Delta = 2.36\ cm \ \ \Rightarrow\ \ \tan^{-1}\left(\frac{2.36}{286}\right) = 0.47\ ^o[/math]