A square window has an area of 196 cm². A curtain is to be made that is 1.5 times the length of one side of the window. What is the required length of the curtain?

The area of a square is given by the formula $A = s^2$, where $s$ is the side length.
Given the area $A = 196 \text{ cm}^2$.

$$s^2 = 196 \text{ cm}^2$$

To find $s$, take the square root of 196.

$$s = \sqrt{196} \text{ cm}$$ $$s = 14 \text{ cm}$$

The length of one side of the window is $14 \text{ cm}$.

The curtain length is 1.5 times the length of one side of the window.
Curtain length $= 1.5 \times s$
Curtain length $= 1.5 \times 14 \text{ cm}$
Curtain length $= 21 \text{ cm}$

The required length of the curtain is $\text{21 cm}$.