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Learn Geometry and Trigonometry Angles and triangles

Angle relationships

A few rules solve most angle problems.

Geometry and Trigonometry: Angles and triangles

Angles on a straight line add to $18 0^{\circ}$ .
Angles around a point add to $36 0^{\circ}$ .
Vertical angles are equal.
Angles in a triangle add to $18 0^{\circ}$ .

Work through it

Two angles on a line: one is $11 0^{\circ}$ .

$180 - 110 = 70$ , so the other is $7 0^{\circ}$ .

A triangle has angles $5 0^{\circ}$ and $6 0^{\circ}$ .

$180 - 50 - 60 = 70$ , so the third is $7 0^{\circ}$ .

Watch out for this

Vertical angles add to $18 0^{\circ}$ .

Vertical angles are equal. Angles side by side on a line add to $18 0^{\circ}$ .

Your turn

NextThe Pythagorean theorem

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