##### Across

**1.**The letters of ancient Greece, which are frequently used in math and science and denoted by Ψ ψ.**6.**For a triangle, this is the point at which the three medians intersect.**8.**The number 10 to the power 100,this number can be written as a 1 followed by 100 zeros.**10.**A sphere-like surface for which all cross-sections are ellipses.**13.**A curve shaped like a spring, it can be made by coiling a wire around the outside of a right circular cylinder.**16.**The four sections into which the x-y plane is divided by the x- and y-axes.**18.**A helping theorem.It is proven true, just like a theorem, but is not interesting or important enough to be a theorem. It is of interest only because it is a stepping stone towards the proof of a theorem.**21.**Similar geometric figures that share a common center.**22.**A part of a line starting at a particular point and extending infinitely in one direction.**23.**A statement accepted as true without proof, it should be so simple and direct that it seems to be unquestionably true.**24.**Set The set with no elements. The empty set can be written or {} and also known as empty set.**26.**Measurement of geometric figures and includes length, angle measure, area, volume.**27.**Quadrilateral with two pairs of adjacent sides that are congruent,also it's diagonals are perpendicular.**28.**A polygon with eleven sides.**29.**A family of related curves usually expressed in polar coordinates. The cardioid is a special kind in it.**31.**a doughnut shape. It is a surface of revolution obtained by revolving (in three dimensional space) a circle about a line which does not intersect the circle.

##### Down

**2.**A three dimensional solid consisting of all points equidistant from a given point. This point is the center of the geometrical figure and all cross-sections are circles.**3.**A polynomial with two terms which are not like terms.eg 2x – 3, 3x5 +8x4, and 2ab – 6a2b5.**4.**A special case of a more general theorem which is worth noting separately. For example, the Pythagorean theorem is a ______ of the law of cosines.**5.**A mathematical sentence built from expressions using one or more equal signs (=).**7.**A parallelogram with four congruent sides and the diagonals are perpendicular.**9.**Any polyhedron with six faces, all of which are quadrilaterals,a regular geometric figure is a cube.**11.**The letters of ancient Greece, which are frequently used in math and science and denoted by Σ σ.**12.**A transformation that is invariant with respect to distance. That is, the distance between any two points in the pre-image must be the same as the distance between the images of the two points.**14.**A polyhedron with six faces, all of which are parallelograms.**15.**The eight regions into which three dimensional space is divided by the x-, y-, and z-axes.**17.**The property of real numbers which guarantees that for any two real numbers a and b, exactly one of the following must be true: a < b, a = b, or a > b.**19.**A line segment, line, or plane that divides a geometric figure into two congruent halves.**20.**A polygon with ten sides.**25.**A number which is a multiply by five.**30.**A rectangular (or square) array of numbers, it can be written using brackets or parentheses.