Which of these equations gives the value of a2?

The formula for the sum of interior angles of a polygon with $n$ sides is $(n-2) \times 180^\circ$.
For a pentagon, $n=5$.

The given angles are $x^\circ$, $2x^\circ$, $3x^\circ$, $4x^\circ$, and $5x^\circ$. Their sum must equal $540^\circ$.

The value of $x$ is $\boxed{36^\circ}$.

a) Calculate each angle of the Polygon.
Substitute $x=36^\circ$ into each angle expression:

• First angle: $x = \mathbf{36^\circ}$
• Second angle: $2x = 2 \times 36^\circ = \mathbf{72^\circ}$
• Third angle: $3x = 3 \times 36^\circ = \mathbf{108^\circ}$
• Fourth angle: $4x = 4 \times 36^\circ = \mathbf{144^\circ}$
• Fifth angle: $5x = 5 \times 36^\circ = \mathbf{180^\circ}$

b) Which is the largest angle?
Comparing the calculated angles ($36^\circ, 72^\circ, 108^\circ, 144^\circ, 180^\circ$), the largest angle is $\mathbf{180^\circ}$.

c) Sketch the pentagon.
A pentagon with an interior angle of $180^\circ$ is a degenerate polygon, meaning three of its vertices are collinear. This makes it appear like a quadrilateral with one vertex lying on one of its sides.

Here is a sketch:

      V4 ----- V3
     /          \
    /            \
   V5 ----------- V2
    \            /
     \          /
      \        /
       \      /
        \    /
         V1

In this sketch, imagine $V_1, V_2, V_3, V_4, V_5$ are the vertices. If $\angle V_3 = 180^\circ$, then $V_2, V_3, V_4$ would lie on a straight line.
A more accurate representation of a pentagon with a $180^\circ$ angle would be:

      V4 ----- V3 ----- V2
     /                   /
    /                   /
   V5 ----------------- V1

Here, $V_4, V_3, V_2$ are collinear, making the angle at $V_3$ equal to $180^\circ$. The sides are $V_1V_2$, $V_2V_3$, $V_3V_4$, $V_4V_5$, and $V_5V_1$.