There are four equal (modulo rotation) parts: three share a corner with the original triangle and a fourth in the middle does not share a corner with the origin

There are four equal (modulo rotation) parts: three share a corner with the original triangle and a fourth in the middle does not share a corner with the original triangle. The one in the middle is highlighted grey as 'the third', the two triangle parts sharing the lower left and lower right corner of the original triangle are ignored and the triangle sharing the top corner of the original triangle is segmented further