LESSON TWENTY-FOURTH.
REVIEW.
Name eight isosceles triangles. (Diagram [19].)
Why is Fig. 2 an isosceles triangle?
What is an isosceles triangle?
Name two right-angled isosceles triangles.
Name five acute-angled isosceles triangles.
Name one obtuse-angled isosceles triangle.
Name two isosceles triangles that are also equilateral.
Are all isosceles triangles equilateral?
Name six isosceles triangles that are not equilateral.
What does “equi” mean? “Latus”?
What are equilateral triangles called on account of their equal angles?
Are all equilateral triangles equiangular?
Are all equiangular triangles equilateral?
What are equilateral triangles?
Name four scalene triangles.
Name two right-angled scalene triangles.
Why is Fig. 3 a right-angled triangle? Why scalene?
What is a scalene triangle?
Name one obtuse-angled scalene triangle.
Name one acute-angled scalene triangle.
PROBLEMS.
From the same point draw two straight lines of any length, making an acute angle with each other.
Make them equal to each other by measuring.
Join their ends.
What kind of a triangle is it on account of its angles?
On account of its two equal sides?
Write its two names inside of it.
Draw an isosceles triangle whose equal sides shall each be less than the third side.
Write its two names within it.
Draw an oblique straight line twice as long as any short measure or unit.
At one end draw a straight line perpendicular to it, and three times as long as the same measure.
Connect the ends of the two lines by a straight line.
What kind of an angle is that opposite the last line drawn?
Are any two of its sides equal?
Write its two names under it.
Draw a horizontal straight line of any length.
At one end draw a vertical line of equal length.
Complete the triangle, and write two names inside.
Draw a right-angled triangle whose base is of any length, and its perpendicular twice as long.
Draw a right-angled triangle whose base is three times as long as any short measure, and its perpendicular five times as long as the same measure or unit.
Diagram 20.
QUADRILATERALS.
How many sides has the figure a b d c?
What is it called on account of the number of its sides?
Name three other quadrilaterals whose vertices are marked.
Name seven by numbers.
Quadrilaterals are sometimes named by means of two opposite vertices.
The quadrilateral a b d c, or c d b a, may be read a d, or b c, or c b, or d a.
Name the quadrilateral, g h f e, four ways.
How many angles has each figure?
On account of the number of their angles they are called quadrangles.
Has the quadrilateral a d any two sides parallel to each other?
Then it is called a trapezium.
A trapezium is a quadrilateral that has no two sides parallel.
Name two other trapeziums.
Why is Fig. 7 a trapezium?
Has the quadrilateral e h any two sides parallel? Which two? Are the other two sides parallel?
It is called a “trapezoid.”
“Oid” means like. What does “trapezoid” mean?
A trapezoid is a quadrilateral that has only one pair of sides parallel.
Name another trapezoid.
Why is Fig. 6 a trapezoid?
How many pairs of parallel sides has the quadrilateral i l?
Name the horizontal parallels.
Name the oblique parallels.
It is called a “parallelogram.”
A parallelogram is a quadrilateral whose opposite sides are parallel.
Name five other parallelograms.
Why is Fig. 4 a parallelogram?
Why is not Fig. 6 a parallelogram?
Why is not e h a parallelogram?
What two names may you give to Fig. 5?
Why is it a quadrilateral? Why a trapezium?
What two names may we give to Fig. 6?
Why is it a quadrilateral? Why a trapezoid?
What two names may we give to Fig. 3?
Why is it a parallelogram? Why a quadrilateral?
