This question is quite vague – a useful feature in my opinion! Describing the area of the triangle as “slightly smaller” means that there are many possible correct areas. Students are not intimidated and willing to try to make a triangle.
The task is also able to be differentiated to many levels. At the most basic, students can draw accurate triangles and count squares and parts of squares. Students who know how to find areas of right-angled triangles using the formula (1/2)bh can draw these. To find the final side length requires Pythagoras, though the teacher can decide not to request this. More advanced students can draw triangles and find their areas using the formula (1/2)ab sinC. Finding the third side length of these triangles requires the cosine rule.
This is great starter or ender to lessons. It can be used to consolidate or review area concepts.
Do you like vague questions?