You may get two to three questions from Geometry in the GMAT quant section. Usually tested as a problem solving variant, you could occassionally come across a data sufficiency question testing core concepts in geometry.
Basics of geometry including properties of triangles, similar triangles, quadrilaterals, polygons and circles are often tested in the GMAT Math Section. Make sure that you do not just memorize the formulae or the theorem. Though you will never be tested on derivations of the theorem, going through the derivations and proofs helps understand concepts better and therefore, solve questions with ease. Wizako's GMAT Math Lesson Book in this chapter covers the following concepts:
Here is a typical solved example in Wizako's GMAT Book from this chapter
In ΔABC, AB = 4.5, AC = 6 and BC = 7.5. The points D & E lie on the line segment BC with BD = 1.5 and EC = 3. What is the value of the ∠DAE?
ΔABE is an isosceles triangle. (Two sides AB and BE are equal)
Therefore, corresponding angles opposite to AB and BE will be equal. i.e., ∠BAE = ∠BEA = ∠DEA (∠BEA is the same as ∠DEA )
Similarly, Δ ACD is also an isosceles triangle. (Two sides AC and DC are equal).
So, corresponding angles opposite to AC and DC will be equal. i.e., ∠DAC = ∠ADE
In triangle ADE, ∠ADE + ∠DEA + ∠DAE = 180°
=> ∠DAC + ∠BAE + ∠DAE = 180°
=> (90° + ∠DAE) + ∠DAE = 180°
=> ∠DAE = 45°
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