Figure 4-17.-Equilateral triangle on a given inscribed
circle: another method.
circle. Draw AB parallel to the horizontal center
line of the circle and tangent to the circumference.
Then use a 30 0/600 triangle to draw AC and BC
at 60° to AB and tangent to the circle.
Another method of accomplishing this
construction is shown in figure 4-17. Draw radii
at 30° to the horizontal center line of the circle,
intersecting the circumference at C and B. There
is a third point of intersection at A, so you now
have three radii: OA, OB, and OC. Draw the sides
of the triangle at A, B, and C, tangent to the
circle and perpendicular to the relevant radius.
RECTANGLE: GIVEN
LENGTH AND WIDTH
To construct a rectangle with a given length
and width, draw a horizontal line AB, equal to
the given length. With a straightedge and triangle,
erect perpendiculars from A and B, each equal
to the given width. Connect the ends of the
perpendiculars.
SQUARE: GIVEN LENGTH OF SIDE
You can construct a square with a given length
of side by the method described for constructing
a rectangle. Another method is shown in figure
4-18. With a T square, draw horizontal line AB
equal to the given length of side. With a T square
and a 45° triangle, draw diagonals from A and
B at 45° to AB. Erect perpendiculars from
A
Figure 4-18.-Square with a given length of side.
and B, intersecting the diagonals. Then
connect the points of intersection.
SQUARE: GIVEN
LENGTH OF DIAGONAL
Figure 4-19 shows a method of constructing
a square with a given length of diagonal. Draw
horizontal line AB, equal to the given length of
the diagonal. Locate O at the center of AB,
and lay off CD through O, perpendicular to and
Figure 4-19.-Square with a given length of diagonal.
4-6
