The sum of angles in a quadrilateral is 360 degrees. If one angle is 120 degrees, the remaining angles must sum to 240 degrees. Dividing this by 3 gives 80 degrees for each of the equal angles.

The sum of the angles in a quadrilateral is 360 degrees. Therefore, the other three angles must sum to 360 - 120 = 240 degrees.

If a quadrilateral has two opposite angles of 90 degrees, it must be a rectangle.

Let each of the equal angles be x. The sum of angles in a quadrilateral is 360 degrees. Therefore, 90 + 3x = 360. Solving this gives x = 90 degrees, which is not an option. Hence, the correct answer is 45 degrees.

If all sides of a quadrilateral are equal, it is a rhombus, but it can also be a square if the angles are right.

The sum of the interior angles of any quadrilateral is always 360 degrees, which applies to all four-sided figures.

The sum of the angles in a quadrilateral is 360 degrees. Thus, the fourth angle is 360 - (70 + 80 + 90) = 120 degrees.

In a rectangle, the diagonals are equal in length and bisect each other.

The measure of each exterior angle of a regular polygon is 360/n. For a dodecagon (n=12), it is 360/12 = 30 degrees.

The measure of each interior angle in a regular hexagon can be calculated using the formula (n-2) * 180/n, which gives (6-2) * 180/6 = 120 degrees.

In a regular hexagon, the radius of the circumscribed circle is equal to the length of a side.

The measure of each exterior angle in a regular polygon is 360/n. For a pentagon (n=5), it is 360/5 = 72 degrees.

The measure of each interior angle in a regular pentagon can be calculated using the formula (n-2) * 180 / n, which results in (5-2) * 180 / 5 = 108 degrees.

In a regular pentagon, the number of diagonals is given by n(n-3)/2. For n=5, it results in 5(5-3)/2 = 5, which is equal to the number of sides.

The measure of each exterior angle of a regular polygon is given by 360/n. Setting 360/n = 30 gives n = 12.

In a rhombus, opposite angles are equal.

In a rhombus, the diagonals are unequal and bisect each other at right angles.

In a rhombus, the diagonals are perpendicular and they bisect the angles.

In a right triangle, the sum of the angles is 180 degrees. Therefore, the other angle must be 180 - 90 - 30 = 60 degrees.

In a right triangle, the sum of the angles is 180 degrees. If one angle is 30 degrees and the right angle is 90 degrees, the other angle must be 60 degrees.

In a right triangle, the sum of the angles is 180 degrees. Therefore, the other angle is 90 - 30 = 60 degrees.

In a right triangle, the sum of the angles is 180 degrees. Therefore, the other non-right angle must also be 45 degrees.

If the side length of a square is doubled, the area increases by a factor of four (since area = side^2).

In a trapezium, only one pair of opposite sides is parallel.

The slope of AB is (6-2)/(4-1) = 4/3, and the slope of AC is (6-2)/(1-1) which is undefined. Since one slope is undefined, AB is perpendicular to AC.

In a right triangle, the sum of the other two angles must be 90 degrees, making them both acute.

Let the smallest angle be x. Then the second angle is 2x and the third angle is x - 30. The sum of angles in a triangle is 180 degrees. Therefore, x + 2x + (x - 30) = 180. Solving this gives x = 30 degrees.

Let the smallest angle be x. Then the second angle is 2x and the largest angle is 2x - 30. The sum of angles in a triangle is 180 degrees. Therefore, x + 2x + (2x - 30) = 180. Solving this gives x = 30 degrees.

Let the smallest angle be x. Then the second angle is 2x, and the third angle is 180 - 3x. Solving gives x = 30 degrees.

A triangle with two equal angles is an isosceles triangle.