I2.1 In square $P Q R S, Y$ is the mid-point of the side $Q R$ and $P X=\frac{3}{4} P Q$.
If $A$ is the ratio of the area of the shaded triangle to the area of the square, find $A$.
$\begin{array}{l}\text { Let } P Q=4 x, P X=3 x, Q X=x, Q Y=Y R=2 x \\ \begin{aligned} A & =\frac{(4 x)^{2}-\frac{1}{2} \cdot 4 x(3 x)-\frac{1}{2} \cdot x(2 x)-\frac{1}{2} \cdot 4 x(2 x)}{(4 x)^{2}} \\ & =\frac{5}{16}\end{aligned}\end{array}$