Explicație pas cu pas:
AD= AB+BC+CD <=> 14= 3+8+CD <=> 14= 11+ CD => CD= 3 => CD=AB
M= mij. AD => AM= MD; AM = 14/2= 7 => MD= 7cm
AM= AB+BM <=> 7= 3+4 <=> 7=7(A) => M=mij. AD si BC
4[tex]BM^{2}[/tex] = 2[tex]AB^{2}[/tex] + 2[tex]BD^{2}[/tex] - [tex]AD^{2}[/tex] <=> 4 x [tex]4^{2}[/tex] = 2 x [tex]3^{2}[/tex] + 2 x [tex]11^{2}[/tex] - [tex]14^{2}[/tex] <=> 4 x 16= 2 x 9 + 2 x 121 - 196 <=> 64= 18+242-196 => 64= 260-194 => 64=64 (A)
