(a+7)²=

To expand the expression \((a + 7)^2\), you use the formula for the square of a binomial:

\[ (a + b)^2 = a^2 + 2ab + b^2 \]

In this case, \(a\) is \(a\) and \(b\) is \(7\).

Applying the formula, we get:

\[ (a + 7)^2 = a^2 + 2 \cdot a \cdot 7 + 7^2 \] \[ = a^2 + 14a + 49 \]

So, \((a + 7)^2 = a^2 + 14a + 49\).