Question

can u tell me why he could not draw it

Answer 1

If we draw a diagonal LY, It will form 2 triangles. To form a triangle we have rules for sides. They are, the sum of two sides of a triangle should be greater than the other side & the difference of to sides should be less than other side. Let's implement this.

The triangles formed by drawing LY are triangle LYA & LYP.
The rules to form a triangle which are mentioned above suits for triangle LYA but for triangle LYP. Because sum of PL & PY = 3+2 = 5 cm which is not equal to the other side, LY which is 6 cm