Answer: Â length = 12
Step-by-step explanation:
Use Pythagorean Theorem: length² + height² = hypotenuse²
length = L
height = L - 7
hypotenuse = L + 1
    L² + (L - 7)² = (L + 1)²
L² + L² - 14L + 49 = L² + 2L + 1
  2L² - 14L + 49 = L² + 2L + 1
   L² - 14L + 49 = 2L + 1
   L² - 16L + 49 = 1
   L² - 16L + 48 = 0
   (L - 4)(L - 12) = 0
 L - 4 = 0   L - 12 = 0
  L = 4       L = 12
Input L = 4 and L = 12 to find the height:
Height = L - 7 Â Â Â Â Â Â height = L - 7
      = 4 - 7             = 12 - 7
      =  -3              = 5
       ↓
negative height is not valid
So, the only valid solution is L = 12