CtgABD₂=│AB│:│AD₂│
│AB│=│A₁B₁│=4
│AD₂│²= │A₁D₂│²+ │AA₁│²
│AA₁│ = 2√7
│A₁D₂│ = │A₁A₂│ + │A₂D₂│
│A₁A₂│ = 2
│A₂D₂│ = │A₁D₁│ - │A₁A₂│ - │D₂D₁│
│A₁D₁│=11
│A₁A₂│=2
│D₂D₁│=5
│A₂D₂│=11-2-5=4
│A₁D₂│ = │A₁A₂│ + │A₂D₂│=2+4=6
│AD₂│²= │A₁D₂│²+ │AA₁│²=6²+(2√7)²=64
│AD₂│²=64
│AD₂│=√64=8
ctgABD₂=│AB│:│AD₂│;│AB│=4;│AD₂│=8
ctgABD₂=4:8=1/2
ctgABD₂=1/2