Answer :
Treat this situation as a right-angled triangle. I have attached a picture below.
cos θ = [tex] \frac{4}{7} [/tex]
⇒ θ = [tex]\cos^{-1}\frac{4}{7} [/tex]
= 55° 2s.f.
cos θ = [tex] \frac{4}{7} [/tex]
⇒ θ = [tex]\cos^{-1}\frac{4}{7} [/tex]
= 55° 2s.f.