For isothermal process, PV= constant
Differentiating both side PdV+VdP=0 or dVdP=V−P
Again for adiabatic process, PVγ= constant
Again differentiating both side dPVγ+γVγ−1dVP=0 or dVdP=−VP×γ ∴ slope of adiabatic curve =γ× slope of isothermal curve