Geometry

What are complementary angles?

• Complementary angles add up to 90°.

• Adjacent complementary angles share a common vertex and arm.

• Example: If angle B1=40°B_1 = 40°B1​=40° and angle B2=50°B_2 = 50°B2​=50°, then B1+B2=90°B_1 + B_2 = 90°B1​+B2​=90°.

• B1B_1B1​ is the complement of B2B_2B2​.

What are supplementary angles?

• Supplementary angles add up to 180°.

• Adjacent supplementary angles share a common vertex and arm.

• Example: If angle B1=130°B_1 = 130°B1​=130° and angle B2=50°B_2 = 50°B2​=50°, then B1+B2=180°B_1 + B_2 = 180°B1​+B2​=180°.

• B1B_1B1​ is the supplement of B2B_2B2​.

What is the property of adjacent angles on a straight line?

• Adjacent angles on a straight line are supplementary.

• If ABCABCABC is a straight line, then B1+B2=180°B_1 + B_2 = 180°B1​+B2​=180°.

• Acceptable reason: adjacent ∠s on a straight line.

• If B1+B2=180°B_1 + B_2 = 180°B1​+B2​=180°, then ABCABCABC is a straight line.

What do vertically opposite angles equal when two lines intersect?

Vert opp ∠s =

What is the sum of angles around a point?

They add up to 360°.
∠s round a point

What is true about corresponding angles when lines are parallel?

They are equal in size.

• Corresp ∠s ; AB ∥ CD

• OR Corresp ∠s =

What is true about alternate angles between parallel lines?

They are equal in size.

• Alt ∠s ; AB ∥ CD

• OR Alt ∠s =

What is true about co-interior angles between parallel lines?

They are supplementary (add up to 180°).

• Co-int ∠s ; AB ∥ CD

• OR Co-int ∠s suppl