Select the alternative which represents three out of the five alternative…

In a 'figure formation' reasoning question, the offered pieces are alternative fragments of a single dissection of the target shape. A set of three pieces is correct only when, placed edge-to-edge, it satisfies all of the following:

• Every touching edge has the same length, and the angles meeting at each joint fit together exactly.

• The three pieces cover the target shape completely, with no gap and no overlap.

• Each piece is used exactly once — decoys are usually near-duplicates of a genuine piece with a slightly different angle or arm length, so they must be ruled out by matching edges and angles, not by the outline alone.

Here the target is an equilateral triangle. Cutting it as shown below: a line near the top separates a small triangle at the apex — this is figure 2. The remaining region is then split by a bent line running from that same cut point down to the triangle's bottom-left corner. The bend produces two pieces sharing this notched edge — a quadrilateral occupying the lower-right area (figure 3) and a notched, concave quadrilateral occupying the lower-left area (figure 4). Fitting figure 2 along the top cut, and figures 3 and 4 along the bent line and the remaining sides, reconstructs the full equilateral triangle exactly, as shown below.

Checking the two unused pieces confirms they do not belong: figure 1 belongs to the same notched, concave family as figure 4, but its notch angle and arm lengths do not match the notch cut into the triangle, so it cannot take figure 4's place without leaving a gap or an overlap along the base. Figure 5 is a shallow, elongated triangle whose widest angle is far greater than the roughly 60 degree corner angles of an equilateral triangle, so it cannot substitute for the apex piece or either quadrilateral piece without extending past the triangle's boundary.

Only figures 2, 3 and 4 satisfy the edge-and-angle match simultaneously, so they are the three pieces that form the equilateral triangle — option 234.