In a vertical plane at `30^@` from the magnetic meridian, the horizontal component is
`H'=Hcos30^@`
While verticale component is still `V`. Therefore, apparent dip will be given by
`tantheta'=V/H'=V/(Hcos30^@)`
`But, V/H=tantheta(where theta=true angle of dip)`
`: tantheta'=(tantheta)/(cos30^@)`
`:. theta=tan^-1[tantheta'cos30^@]`
`=tan^-1[(tan45^@)(cos30^@)]`
`=41^@`