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# Test yourself now

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## 11.5 Chapter summary

• A triangle is a polygon with three straight sides and three interior angles.
• The sum of the interior angles of a triangle is equal to $$180^{\circ}$$.
• A scalene triangle has no equal sides. All sides are different lengths and all angles are different sizes.
• An isosceles triangle has two equal sides. The two angles opposite the equal sides are also equal.
• An equilateral triangle has three equal sides. All three sides are the same length and all three interior angles are equal to $$60^{\circ}$$.
• An acute-angled triangle has all interior angles less than $$90^{\circ}$$.
• A right-angled triangle has one interior angle equal to $$90^{\circ}$$. The side opposite the right angle is called the hypotenuse and it is the longest side of the triangle.
• An obtuse-angled triangle has one interior angle greater than $$90^{\circ}$$ and less than $$180^{\circ}$$.
• The exterior angle of a triangle is equal to the sum of the two interior opposite angles.
• A quadrilateral is a four-sided polygon.
• The sum of the interior angles of a quadrilateral is $$360^{\circ}$$.
• A parallelogram is a quadrilateral with both pairs of opposite sides equal and parallel.
• A rectangle is quadrilateral with opposites equal and parallel and interior angles equal to $$90^{\circ}$$.
• A square is parallelogram with all sides equal and interior angles equal to $$90^{\circ}$$.
• A rhombus is a quadrilateral with both pairs of opposite sides parallel and all sides equal. Two pairs of opposite angles are equal.
• A trapezium is a quadrilateral with one pair of opposite sides parallel.
• A kite is a quadrilateral with two pairs of adjacent sides equal.
• Two shapes are congruent if they are the same shape and size.
• Two shapes are similar if they are the same shape, but they may be different sizes.
• Two shapes are similar if corresponding angles are equal and corresponding sides are in the same proportion.