Zadanie 51 CKE zbiór zadań z matematyki poziom podstawowy

Task 51 CKE Math Problem Set, Basic Level Each edge of the tetrahedron 𝐴𝐵𝐶𝑆 has length 𝑎. Points 𝐷 and 𝐸 are the midpoints of sides 𝐴𝐶 and 𝐵𝐶, respectively (see figure). Calculate the area of ​​triangle 𝑫𝑬𝑺. Record your calculations.