Use the formula (a−b)² = a² − 2ab + b².

Here, $a=7a^2$ and $b=b^5$.

$$(7a^2 - b^5)^2 = (7a^2)^2 - 2(7a^2)(b^5) + (b^5)^2$$

$$= 49a^4 - 14a^2b^5 + b^{10}$$

The simplified expression is $\boxed{49a^4 - 14a^2b^5 + b^{10}}$.

m)

Here, $a=\frac{x}{2}$ and $b=1$.

$$\left(\frac{x}{2} - 1\right)^2 = \left(\frac{x}{2}\right)^2 - 2\left(\frac{x}{2}\right)(1) + 1^2$$

$$= \frac{x^2}{4} - x + 1$$

The simplified expression is $\boxed{\frac{x^2}{4} - x + 1}$.

n)

Here, $a=\frac{x}{2}$ and $b=3$.

$$\left(\frac{x}{2} - 3\right)^2 = \left(\frac{x}{2}\right)^2 - 2\left(\frac{x}{2}\right)(3) + 3^2$$

$$= \frac{x^2}{4} - 3x + 9$$

The simplified expression is $\boxed{\frac{x^2}{4} - 3x + 9}$.

o)

Here, $a=\frac{y}{5}$ and $b=1$.

$$\left(\frac{y}{5} - 1\right)^2 = \left(\frac{y}{5}\right)^2 - 2\left(\frac{y}{5}\right)(1) + 1^2$$

$$= \frac{y^2}{25} - \frac{2y}{5} + 1$$

The simplified expression is $\boxed{\frac{y^2}{25} - \frac{2y}{5} + 1}$.