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Lines, Angles, and Triangles

SAT Math· difficulty 4/5

In right triangle ABC with the right angle at C, cosA=frac45\\cos A = \\frac{4}{5}. If AC = 12, what is the length of AB?

  • A

    15

    check_circle
  • B

    20

  • C

    9

  • D

    485\frac{48}{5}

Explanation

cosA=fracACAB=frac45\\cos A = \\frac{AC}{AB} = \\frac{4}{5}. So frac12AB=frac45\\frac{12}{AB} = \\frac{4}{5}, giving AB=15AB = 15.

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