Square Area Function: Express Area with Side Length 'a'

To determine the area of a square given its side length, we utilize the fundamental formula for the area of a square:

• Step 1: Recall that the area $A$ of a square with side length $a$ is given by the formula $A = a^2$.
• Step 2: Translate this into a function form, identifying the area as $y$.
• Step 3: Write the function expressing the area: $y = a^2$.

To conclude, the area of the square can be expressed as the function $y = a^2$.

Out of the provided choices, the correct expression for the area of the square as a function of the side length $a$ is Choice 4: $y = a^2$.