Formulas:
Area = π × r²
Perimeter = 2 × π × r
Area = a²
Perimeter = 4 × a
Area = w × h
Perimeter = 2 × (w + h)
Let s = (a + b + c)/2
Area = √[s(s–a)(s–b)(s–c)]
Perimeter = a + b + c
Area = π × a × b
Perimeter ≈ π[3(a+b) – √((3a+b)(a+3b))]
Area = b × h
Perimeter = 2(b + s)
Area = ((a + b)/2) × h
Perimeter = a + b + c + d
Area = (n × s²)/(4 × tan(π/n))
Perimeter = n × s