In ∆ABC, ∠B = 90° , and l(BC) = 21, and l(AB) = 20
∴ According to Pythagoras’ theorem,
∴ l(AC)2 = l(BC)2 + l(AB)2
∴ l(AC)2 = 212 + 202
∴ l(AC)2 = 441 + 400
∴ l(AC)2 = 841
∴ l(AC)2 = 292
∴ l(AC) = 29
Perimeter of ∆ABC = l(AB) + l(BC) + l(AC)
= 20 + 21 + 29
= 70
∴ The length of hypotenuse AC is 29 units, and the perimeter of ∆ABC is 70 units.
