good day

can you help me please I have homework and Icann't solution

the homework is proof that the inequality :

Double integral (from a to b)(from c to d) of ( f(x,y) (∂^2f(x,y)/∂x∂y))dy dx <= ((b-a)(d-c))/8 double integral (from a to b)(from c to d) of (∂^2f(x,y)/∂x∂y))^2 dy dx

and thank you for help me.