Explanation:
a midsegment is the line segment connecting the midpoints of two sides of a triangle. Since a triangle has three sides, each triangle has three midsegments (that create the midsegment triangle). A triangle midsegment is parallel to the third side of the triangle and is half of the length of the third side (due to similar triangles and their constant scaling factors, when one side of the similar triangle is half of the sys of the original triangle, then all its sides are half of their original counterparts).
the 3 sides of the main triangle are
2x + 5
3x - 1
5x
the perimeter of the main triangle is the sum of these :
2x + 5 + 3x - 1 + 5x = 10x + 4
since the sides of the midsegment triangle are all exactly half the length of the sides of the main triangle, also the perimeter of the midsegment triangle is half of the perimeter of the original triangle :
(10x + 4) / 2 = 5x + 2