Geometry, For GMAT Notes | Study Quantitative Reasoning for GMAT - GMAT

GEOMETRY 

WHY you need to know Geometry:

1. 4- 9 Geometry questions show up on the GMAT. 2. Geometry is based on a series of simple formulas. Knowing the formulas makes the questions easy to answer.
Note: If a Problem Solving question includes a drawing, then that drawing is usually to scale and can be used for estimation purposes (unless the question states that the figure is NOT drawn to scale). Note: If a Data Sufficiency question includes a drawing, then you should NOT TRUST IT. Some DS drawings are completely off; as such, they can not be used for estimation purposes. You can trust whatever numbers or descriptions you are given, but be suspicious of any picture that comes with a DS question.

Lines
Questions involving straight lines will likely include one or more of the following rules: 1. Lines add up to 180° 2. When lines criss-cross, opposite angles equal one another 3. Parallel lines, when crossed by a third line, will have the same set of 2 angles show up 4 times 4. Perpendicular lines form 90° angles at their meeting point

Triangles

Triangle questions will involve major rules and sometimes minor rules. Be on the lookout for each of these specific ideas on the GMAT: Major Rules: 

Major Rules:

1. Triangles add up to 180° 

2. Area = 

3. Pythagorean Theorem: 

4. Common Pythagorean triples:
• 3, 4, 5 
• 5, 12, 13 
5. Multiples of those triples for example:
• 9, 12, 15 
• 50, 120, 130 
6. 30°, 60°, 90° Triangle
7. 45°, 45°, 90° Triangle 

Sometimes the following concepts show up; not every one will, but if they show, then you need to be ready for them.

Minor Rules:

1. Isosceles Triangles – 2 sides and 2 corresponding angles are equal
2. Equilateral Triangles – 3 sides are equal, all angles are 60 degrees
3. Hidden Right Triangles – in squares or equilateral triangles
4. Triangle Inequality Theorem – with 2 sides, you can figure out the minimum length of the third side (greater than the difference of the numbers) and the maximum (less than the sum of the numbers)