Parallelograms on equal bases and between the. same parallels, are equal.

Triangles upon the same base and between the same parallels, are equal.

PROP. XXXVIII. THEOR.

Triangles upon equal bases and between the same parallels, are equal.

PROP. XXXIX. THEOR.

Equal triangles upon the same base and on the same side of it, are between the same parallels.

Equal triangles on equal bases, in the same right line, and on the same side of it, are between the same parallels.

PROP. XLI. THEOR.

If a parallelogram and a triangle are upon the same base and between the same parallels, the parallelogram is double of the triangle.

To construct a parallelogram equal to a given triangle, and having an angle equal to a given rectilinear angle.

PROP. XLIII. THEOR.

The complements of the parallelograms which are about the diagonal of a parallelogram, are equal.

To a given straight line to apply a parallelogram equal to a given triangle, and having an angle equal to a given rectilinear angle.

PROP. XLV. PROB.

To construct a parallelogram equal to a given rectilinear figure, and having an angle equal to a given rectilinear angle.

PROP. XLVI. PROB.

Upon a given straight line to construct a square.