1600SAT Logo All SAT Skills
    Geometry & TrigonometryMedium

    Lines, angles, and triangles

    Apply angle relationships — including parallel lines, transversals, and triangle properties — to find missing measurements.

    Sample SAT Problem

    Two parallel lines are cut by a transversal. One angle is 65°. What is the co-interior (same-side interior) angle?

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    Step-by-Step Solution

    Co-interior angles are supplementary: 180° − 65° = 115°.

    Key Tips from Pamela

    • Alternate interior angles are equal; co-interior angles are supplementary.
    • The exterior angle of a triangle equals the sum of the two non-adjacent interior angles.
    • Triangle inequality: the sum of any two sides must be greater than the third.

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