Question

Fill in the blank with a number to make the expression a perfect square y^2 -18y+

Answer 1

Given,

The expression is,

$y^2-18y+--$

Required

The perfect square of the expression.

To make the perfect square add 81 to the expression.

$\begin{gathered} y^2-18y+81 \\ =(y)^2-2\times y\times9+(9)^2 \\ =(y-9)^2 \end{gathered}$

hence, it is required to add 81.