Prerequisites:
Rectangle (definition)
Properties of parallelogram (proof)
SAS congruence (proof)
Proof:
Let ABCD be a rectangle having diagonals AC and BD, which intersect at a point E.
Now in \triangle ADC and \triangle BCD,
\qquad\quad AD = BC\qquad\qquad\qquad\qquad\qquad\text{(opposite sides of parallelogram are equal)}\\ \qquad\quad DC = DC\qquad\qquad\qquad\qquad\qquad\text{(common)}\\ \qquad\quad\angle ADC = \angle BCD = 90^o\qquad\qquad\:\text{(by definition of rectangle)}
Hence, \triangle ADC\cong\triangle BCD by SAS rule.
Therefore, by CPCTC, AC = BD.
Q.E.D.
Recommended:
Characteristics of parallelogram
Angle sum property of polygon
Area of rectangle
No comments:
Post a Comment