Answer:

Step-by-step explanation:
A quadrilateral is a parallelogram when opposite sides are parallel. This will be the case when ...
- one pair of opposite sides are parallel and the same length (choice B)
- each pair of opposite sides is the same length (choice E)
An isosceles trapezoid has one pair of parallel sides and the other pair of opposite sides the same length, so that is not sufficient to describe a parallelogram. (Choices A and C describe this condition.)
A line segment is always congruent to itself, so that fact establishes nothing about a parallelogram. (choice D)
_____
<em>Comment on opposite sides equal</em>
Choice E can also describe an hourglass-shaped figure. We assume here that the quadrilateral is convex, with no sides crossing each other.
Answer:
Step-by-step explanation:
There are total 7 rectangles of same dimensions.

Answer:
18
Step-by-step explanation:
There are 6 dots. The number of ways we can select 3 from 6 is:
₆C₃ = 6! / (3! (6−3)!)
₆C₃ = 6! / (3! 3!)
₆C₃ = 6×5×4 / (3×2×1)
₆C₃ = 20
However, 2 of these combinations are lines, not triangles.
So there are 18 possible distinct triangles.
18 - 2,3,6,8
24 - 2,4,6,8,12
HCF = 8
Since irrational numbers go on forever, no matter how much you add or multiply rational numbers, irrational numbers remain irrational.