Mathematics Crossword

2. the difference of the upper and lower limits
5. a parallelogram with a right angle
9. a system of equations having no solution are said to be _____
10. by joining the midpoints of all sides of a quadrilateral, a _____ is formed
13. in x²y², "4" is the _____ of the polynomial

1. a line passing through two or more parallel lines
3. a line touching one, singular point on a circle
4. the mean of the upper and lower limits
6. in a semi-circle, both the major segment and sector are _____
7. the intersection-point of all three medians of a triangle
8. the longest chord in a circle
11. a universal truth not needing proof
12. the values in square root that cannot be further simplified into whole numbers or integers