I dont understand the last few steps of this problem:

d2t/dn2= d/dn (d/dn (t))

= d/dn ( q -h/n2+h/n2)

= 2h/n3- 2h/n3= 2h/n3( 1- ) - Student Note: I know up to this point!

Given that ,0 < < 1.0 and n is integer. h is going to be constant

d2t/dn2is going to have positive value.

Which indicates there exist minimum at dt/dn =0

q - h/n2+ h/n2= 0

h(1- ) /n2= q

n =( h(1-) / q )1/2