A
  ] Â
  |
  |_________________
  D                 | B
                   |
                   |
                    C
Let ABCD be this parallelogramÂ
AB + BC + CD + DA = 50, but AD = BCÂ and AB = DC, Then:
2.AD + 2.AB = 50 and :
AD+AB = 25 . We also know that AB+1 = AD (Given), then:
AD + (AD+1) = 25
2.AD = 24Â
AD = 12, THEN AB = 12+1=13
Calculate DB the diagonal perpendicular to AD, using Pythagoras:
AD² + DB² = AB²
12² +DB² = 13²
DB² = 13² - 12² = 25
AND DB= 5