For any Maths and Quantitative Aptitude sum, formulas are those fundamentals which help you to resonate and solve it. In GMAT Quant, this cheatsheet list of formulas for Geometry, will assist you in brushing up your basics.
Perimeter Formulas
Shape  Formula  Where, P = Perimeter and 
Square  \(P = 4s\)  s = Sides 
Rectangle  \(P = 2l + 2w\)  l = Length
w = Width 
Parallelogram  \(P = 2l + 2w\)  l = Length
w = Width 
Trapezoid or Trapezium  \(P = s_{1} + s_{2} + b_{1} + b_{2}\)  \(s_{1}\) and \(s_{2}\) are two sides and \(b_{1}\) and \(b_{2}\) are the two bases of the figure. 
Triangle  \(P = s_{1} + s_{2} + b\)  \(s_{1}\) and \(s_{2}\) are two sides and b = base 
Rhombus  \(P = 4l\)  l = Length 
Area Formulas
Shape  Formula  Where A = Area and 
Triangle  \(A = \frac{1}{2} \times b \times h\)  b = base h = Vertical height 
Square  \(A = a^{2}\)  a = length of side 
Rectangle  \(A = w \times h\)  w = Width h = Height 
Parallelogram  \(A = b \times h\)  b = base h = vertical height 
Trapezoid or Trapezium  \(A = \frac{1}{2} (a + b) \times h\)  a, b = Length if two sides of the figure h = Vertical height 
Circle  \(A = \pi r^{2}\)  r = Radius 
Ellipse  \(A = \pi ab\)  a, b = Longest and Shortest Radius of the figure 
Sector of a Circle  \(A = \frac{1}{2}r^{2}\theta\)  r = Radius \(\theta\) = angle in radians 
Regular npolygon  \(A = \frac{1}{4} \times n \times a^{2} \times \cot \frac{\pi}{n}\)

n = Number of Sides a = Length of the sides 
Surface Area Formulas
Shape  Formula  Where S = Surface Area and 
Rectangular Solid  \(S = 2lh + 2wh + 2wl\)  l = Length h = Heightw = Width 
Cube  \(S = 6s^{2}\)  s = Sides of the Cube 
Right Circular Cylinder  \(S = 2\pi \times rh + 2\pi \times r^{2}\)  h = Vertical Height of the Cylinder r = Radius of the base 
Sphere  \(S = 4\pi \times r^{2}\)  r = Radius 
Right Circular Cone  \(S = \pi \times r \sqrt{r^{2} + h^{2}}\)  h = Vertical height r = Radius of the base 
Torus  \(S = \pi^{2} \times (R^{2} – r^{2})\)  R = Radius of the larger base r = Radius of the smaller base 
Volume Formulas
Shape  Formula  Where V = Volume and 
Rectangular Solid  \(V = lwh\)  l = Length h = Heightw = Width 
Cube  \(V = s^{3}\)  s = Sides of the Cube 
Right Circular Cylinder  \(V = \pi \times r^{2}h\)  h = Vertical Height of the Cylinder r = Radius of the base 
Sphere  \(V = \frac{4}{3} r^{3}\)  r = Radius 
Right Circular Cone  \(V = \frac{1}{3} \pi r^{2}h\)  h = Vertical height r = Radius of the base 
Square or Rectangular Pyramid  \(V = \frac{1}{3} lwh\)  l = Length of the Base h = Vertical heightw = Width of the Base (In Case of Square, bothe l and w will be equal) 
Circle
Circumference of a Circle
\(Circumference \; (C) = \pi d = 2 \pi r\)
Where, d = diameter and r = Radius
Area of a Circle
\(Area \; (A) = \pi r^{2}\)
Where, r = Radius
Pythagoras Theorem
The Pythagorean Theorem states that – The area of the square built upon the hypotenuse of a right triangle is equal to the sum of the areas of the squares upon the remaining sides.
Which implies that in the above Triangle, a and b are the lengths of the two legs of the triangle and c is the length of the hypotenuse of the triangle.
\(a^{2} + b^{2} = c^{2}\)
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