Let PS be the lighthouse of height h meters. Let SQ=x and SR = y.
In
ΔQSP,
tanα=SPSQ
tanα=hx
x=htanα.......(1)
In
ΔRSP,
tanβ=SPSR
tanβ=hy
y=htanβ.......(2)
Distance between the ships =x+y
=(htanα+htanβ)
=h(tanα+tanβtanα.tanβ)
The value of distance between the ships =h(tanα+tanβtanα.tanβ) or h(cotβ+cotα)