$\displaystyle{{9}}^{{2}}={81}\usepackage{cmbright}\Huge\$ , which is less than 88, and $\displaystyle{{10}}^{{2}}={100}\usepackage{cmbright}\Huge\$ , which is greater than 88. The square root of 88 must be between 9 and 10, but there are no whole numbers between 9 and 10, so 88 is not a perfect square.