How many degrees are in a straight line?
180°. If two angles form a straight line (linear pair), they must sum to 180°.
How many degrees are in a full circle?
360°. Any angle formed by rotation around a point must total 360°.
What is the sum of angles in a triangle?
180°. This is fixed for all triangles, regardless of shape.
What is the sum of interior angles of a quadrilateral?
360°. Formula for polygons: (n − 2) × 180°.
Formula for sum of interior angles of n-sided polygon?
(n − 2) × 180°. Example: Pentagon → (5−2)×180 = 540°.
What are vertical angles?
Opposite angles formed by intersecting lines. They are always equal.
What are complementary angles?
Two angles that sum to 90°.
What are supplementary angles?
Two angles that sum to 180°.
If two parallel lines are cut by a transversal, what are alternate interior angles?
They are equal. This is a common EA trap.
Corresponding angles in parallel lines are?
Equal.
What defines an isosceles triangle?
Two equal sides → two equal angles opposite those sides.
What defines an equilateral triangle?
All sides equal → all angles 60°.
What defines a right triangle?
One 90° angle.
Pythagorean theorem?
a² + b² = c² (c is hypotenuse)
Common Pythagorean triples?
3-4-5 5-12-13 8-15-17 Memorize these to avoid squaring.
Area of triangle formula?
(1/2) × base × height.
What is altitude of triangle?
Perpendicular height from base to opposite vertex.
Triangle inequality rule?
Sum of any two sides must be greater than the third.
If sides are 2, 3, and x, what must x satisfy?
1 < x < 5 Because 2+3 > x and |2−3| < x.
If hypotenuse known and one leg known, how find other leg?
Use Pythagorean theorem.
Circumference formula?
C = 2πr
Area of circle formula?
A = πr²
What is diameter in relation to radius?
d = 2r
If diameter doubles, what happens to area?
Area quadruples (since r² effect).