Triangle Perpendicular Side Relation

XAT 2023 · Quantitative Ability & Data Interpretation · Medium · Geometry

ABC is a triangle with BC=5BC=5. D is the foot of the perpendicular from A on BC. E is a point on CD such that BE=3BE=3. The value of AB2−AE2+6CDAB^2 - AE^2 + 6CD is:

  1. A.

    5

  2. B.

    10

  3. C.

    14

  4. D.

    18

  5. E.

    21

Answer

E

Explanation

Let BD=x  ⟹  DE=3−xBD = x \implies DE = 3 - x and CD=5−xCD = 5 - x. In right △ABD\triangle ABD, AB2=AD2+x2AB^2 = AD^2 + x^2. In right △ADE\triangle ADE, AE2=AD2+(3−x)2AE^2 = AD^2 + (3-x)^2. AB2−AE2=x2−(3−x)2=6x−9AB^2 - AE^2 = x^2 - (3-x)^2 = 6x - 9. AB2−AE2+6CD=6x−9+6(5−x)=6x−9+30−6x=21AB^2 - AE^2 + 6CD = 6x - 9 + 6(5-x) = 6x - 9 + 30 - 6x = 21.

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