Geometry for GMAT

 

What you need to remember is that GMAT geometry problems always involve more than one step and that when a GMAT problem offers you just a ratio as answer, without any numbers to start from, you need to plug-in any number in the formulas you use.

Some basic tools refer to remembering number replacement and measurements used by GMAT.

• You need to memorize the following approximations: Π = 3, √1 = 1, √2 = 1.4, √3 = 1.7, √4 = 2
• For those used with the metric system memorize this: 12 inches = 1 foot and 3 feet = 1 yard

Also any drawings that have written next: “not drawn to scale” can not be measured.

Going back to the uses that the people which are not native English speaker:

• Line = straight line that extends without end in both directions
• Line segment = part of a line from one point to another
• Right angle = 90
• Perpendicular lines = two lines intersect at right angles
• Parallel lines = two lines in the same plane that do not intersect
• Polygon = closed plane figure formed by three or more line segments called sides
• Vertices = point of intersection of the sides
• Triangle = 3 sides polygon
• Quadrilateral = 4 sides polygon
• Pentagon = 5 sides polygon
• Hexagon = 6 sides polygon
• 180 degrees = sum of the interior angle measures of a triangle
• (n-2) x 180 degrees = sum of the interior angle measures of a polygon with n sides

Degrees and angles

• 360 degrees = circle.
• 180 degrees = line

When two parallel lines are cut by a third line, there appear to be eight separate angles, but there are really only two.( If you do not understand that, maybe is time for you to “Google” some more)

Triangles

• One side of a triangle can never be longer than the sum of the lengths of the other two sides of the triangle, or less than their difference
• Equilateral = all sides of equal length (the angles are also equal)
• Isosceles = two sides of the same length
• Right triangle = a right angle (opposite side = hypotenuse, the others = legs)
• Perimeter = the sum of the lengths of the three sides
• Area = (base x altitude)

Pythagorean Theorem = in a right triangle, the square of the hypotenuse equals the sum of the squares of the other sides.

a² + b² = c²

3 – 4 – 5; 6 – 8 – 10; 12 – 5 – 13; 12 – 9 – 15

A right isosceles triangle: 45 – 45- 90 = 1: 1: √2

A 30 – 60 – 90 triangle: 1: √3: 2

Circles

• Circle = a set of points in a plane that are all located the same distance from a fixed point (the center)
• Chord = a line segment that has its endpoints on the circle
• Diameter = a chord that passes through the center of the circle
• Radius = a segment from the center of the circle to a point on the circle (r)
• Length of an arc of the circle = the degree of the arc/360
• Tangent to a circle = a line that has exactly one point (point of tangency) in common with a circle
• Circumference = the distance around the circle. C = 2 Π r
• Area A = Πr²

Rectangles, squares and other four-sided objects

• Parallelogram = a quadrilateral with both pair of opposite sides parallel. Area = base x heights
• Rectangle = Parallelogram with right angles. Area = length x width
• Square = rectangle with all sides equal
• Trapezoid = a quadrilateral with two sides that are parallel. Area = small base x big base x height/2

Solids, volume and surface area

• Rectangular solid = a three dimensional figure formed by six rectangular surfaces.
• Area = sum of the areas of all the faces
• Volume = length x width x height

Cylinder

• Area = 2 Π r² + 2 Π r h
• Volume = Π r² h

Coordinate geometry - Coordinate plane

• X – Axis = horizontal line
• Y – Axis = vertical line
• Point 1 = (x1, y1); point 2 = (x2, y2)

Line in a coordinate plane: y = m x + b

b = y- intercept. m = slope.

m (slope) = (y2-y1) / (x2-x1)