Question : basic physics - pushing box up a hill

Hi

If a man is pushing a box up a hill using a horizontal force, why is the angle in the diagram equal to theta? Is it because the angles are alternate angles of a pair of parallel lines (Fpush and the ground are parallel)

thanks

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Answer : basic physics - pushing box up a hill

>> Is it because the angles are alternate angles of a pair of parallel lines
Yes, alternate interior angle theorem:
    http://www.mathsisfun.com/geometry/alternate-interior-angles.html