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Hint: First we will draw a line from A parallel to BC and a line from C parallel to BA. Then we will let them meet at point D and join OD. Then we will prove ABCD is parallelogram as opposite sides are parallel and then prove this parallelogram to be a rectangle by using the basic properties of a rectangle. We will use the property of a rectangle that the diagonal of a rectangle bisect other and are of equal length to prove.
Complete step by step solution: We are given that ABC is a right-angled triangle and O is the midpoint of the side opposite to the right angle.
First, we will draw a line from A parallel to BC and a line from C parallel to BA.
Then we will let them meet at point D and join OD.
First, we will take ABCD, where we know that \[{\text{AB||DC}}\] and \[{\text{BC||AD}}\] by our above construction.
Thus, the opposite sides are parallel.
Hence, ABCD is a parallelogram.
We also know that adjacent angles of a parallelogram are supplementary, from the above diagram, the sum of angle \[\angle ABC\] and \[\angle BCD\] is \[180^\circ \], we have
\[ \Rightarrow \angle ABC + \angle BCD = 180^\circ \]
Substituting the value of \[\angle ABC\] in the above equation, we get
\[ \Rightarrow 90^\circ + \angle BCD = 180^\circ \]
Subtracting both sides by \[90^\circ \] in the above equation, we get
\[
\Rightarrow 90^\circ + \angle BCD - 90^\circ = 180^\circ - 90^\circ \\
\Rightarrow \angle BCD = 90^\circ \\
\]
Also, we know that the opposite angles of a parallelogram are equal, so we have
\[
\Rightarrow \angle DAB = \angle BCD \\
\Rightarrow \angle DAB = 90^\circ \\
\]
\[
\Rightarrow \angle ADC = \angle ABC \\
\Rightarrow \angle ADC = 90^\circ \\
\]
Therefore, each angle of the parallelogram ABCD is a right angle.
So we know that when a parallelogram with all right angles is a rectangle.
Thus, ABCD is a rectangle.
We also know that the diagonals of a rectangle bisect each other, then we have from the above diagram that
\[ \Rightarrow OA = OC = \dfrac{1}{2}AC{\text{ ......eq.(1)}}\]
\[ \Rightarrow OB = OD = \dfrac{1}{2}BD{\text{ ......eq.(2)}}\]
We also know that the diagonal of a rectangle are equal length, then we have
\[ \Rightarrow BD = AC\]
Dividing both sides by 2 in the above equation, we get
\[ \Rightarrow \dfrac{1}{2}BD = \dfrac{1}{2}AC\]
Using equation (1) and equation (2) in the above equation, we get
\[ \Rightarrow OB = OA\]
Therefore, we have found out that \[OB = OA = OC\].
Hence, O is equidistant from A, B and C.
Hence, proved.
Note: In solving these types of questions, you need to know that the properties of rectangles and their diagonals. Then we will use the properties accordingly. This is a simple problem, one should only need to know the definitions. It is clear from the diagram that it is a rectangle as nowhere it is given it to be a square, so remember that as well.
Complete step by step solution: We are given that ABC is a right-angled triangle and O is the midpoint of the side opposite to the right angle.
First, we will draw a line from A parallel to BC and a line from C parallel to BA.
Then we will let them meet at point D and join OD.
First, we will take ABCD, where we know that \[{\text{AB||DC}}\] and \[{\text{BC||AD}}\] by our above construction.
Thus, the opposite sides are parallel.
Hence, ABCD is a parallelogram.
We also know that adjacent angles of a parallelogram are supplementary, from the above diagram, the sum of angle \[\angle ABC\] and \[\angle BCD\] is \[180^\circ \], we have
\[ \Rightarrow \angle ABC + \angle BCD = 180^\circ \]
Substituting the value of \[\angle ABC\] in the above equation, we get
\[ \Rightarrow 90^\circ + \angle BCD = 180^\circ \]
Subtracting both sides by \[90^\circ \] in the above equation, we get
\[
\Rightarrow 90^\circ + \angle BCD - 90^\circ = 180^\circ - 90^\circ \\
\Rightarrow \angle BCD = 90^\circ \\
\]
Also, we know that the opposite angles of a parallelogram are equal, so we have
\[
\Rightarrow \angle DAB = \angle BCD \\
\Rightarrow \angle DAB = 90^\circ \\
\]
\[
\Rightarrow \angle ADC = \angle ABC \\
\Rightarrow \angle ADC = 90^\circ \\
\]
Therefore, each angle of the parallelogram ABCD is a right angle.
So we know that when a parallelogram with all right angles is a rectangle.
Thus, ABCD is a rectangle.
We also know that the diagonals of a rectangle bisect each other, then we have from the above diagram that
\[ \Rightarrow OA = OC = \dfrac{1}{2}AC{\text{ ......eq.(1)}}\]
\[ \Rightarrow OB = OD = \dfrac{1}{2}BD{\text{ ......eq.(2)}}\]
We also know that the diagonal of a rectangle are equal length, then we have
\[ \Rightarrow BD = AC\]
Dividing both sides by 2 in the above equation, we get
\[ \Rightarrow \dfrac{1}{2}BD = \dfrac{1}{2}AC\]
Using equation (1) and equation (2) in the above equation, we get
\[ \Rightarrow OB = OA\]
Therefore, we have found out that \[OB = OA = OC\].
Hence, O is equidistant from A, B and C.
Hence, proved.
Note: In solving these types of questions, you need to know that the properties of rectangles and their diagonals. Then we will use the properties accordingly. This is a simple problem, one should only need to know the definitions. It is clear from the diagram that it is a rectangle as nowhere it is given it to be a square, so remember that as well.
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