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Therefore, area of quadrilateral ABCD = Area of ABC + Area of ACD

=^12 ×^ d^ ×^ h 1 +^12 ×^ d^ ×^ h 2 square units

= 21 d (h 1 + h 2 ) square units

The idea may be explained orally with provision of adequate practice in memorizing

the formula and facilitating the child to do the calculations on his/her own.

The idea may be taught using paper folding also.

14. Sum of the angles of a quadrilateral is 360o
    The sum of the angles of a quadrilateral will always be equal to 360o. If the measure
    of an angle is equal to 360^0 it is also called as angle at a point.

The child may learn this idea by discovery. Construct a quadrilateral on a sheet of

paper to form four angles of some measurement at its vertices. Cut the paper in such

a way that the four angles formed in the vertices are taken apart. Enable the child to

assemble the four papers in such a way that all the four pieces together form an angle

of 360o. Thus the child may be able to understand that in any quadrilateral the sum of

all the four angles formed will always be equal to 360^0.

The Procedure is explained thoroughly in the Creative Mathematics section.

B

D C

A

A + B + C + D = 360 o

A

M

N

D

B C