QUESTION IMAGE
Question
- if ( overline{er} ) is rotated about point ( m ) by ( 30^{circ} ), then which of the following is true about the length of ( overline{er} ) compared to the length of its image, ( overline{er} )?
(1) ( er = 2er )
(2) ( er=\frac{1}{2}er )
(3) ( er = er )
(4) ( er = er + 30 )
- in the image shown, ( overline{hi} ) is the image of ( overline{hi} ) after a clockwise rotation of ( 104^{circ} ) about point ( c ). which of the following distances do not have to be the same?
(1) the distance from ( c ) to ( i ) and the distance from ( c ) to ( h )
(2) the distance from ( c ) to ( h ) and the distance from ( c ) to ( h )
(3) the distance from ( h ) to ( i ) and the distance from ( h ) to ( i )
(4) the distance from ( i ) to ( c ) and the distance from ( c ) to ( i )
- in the figure shown below, ( \triangle qrs ) is the image of ( \triangle mnp ) after a clockwise rotation about point ( c ) by an angle of ( 120^{circ} ). the angles of ( \triangle mnp ) are shown. which of the following must be the measure of ( angle r )?
(1) ( 51^{circ} )
(2) ( 59^{circ} )
(3) ( 70^{circ} )
(4) ( 120^{circ} )
- which of the following would rotate a point in the coordinate grid by ( 90^{circ} ) clockwise about the origin?
(1) ( (x,y)\to(y,x) )
(3) ( (x,y)\to(-x,-y) )
(2) ( (x,y)\to(-y,x) )
(4) ( (x,y)\to(y,-x) )
- if ( overline{wx} ) is rotated by ( 90^{circ} ) counterclockwise about the origin, then its image would have endpoints at
(1) ( w(1,2) ) and ( x(4,8) )
(2) ( w(-1,2) ) and ( x(-4,8) )
(3) ( w(2,-1) ) and ( x(8,-4) )
(4) ( w(-2,1) ) and ( x(8,4) )
Question 1
Step1: Property of rotation
Rotation is a rigid transformation. Rigid transformations preserve the length of segments.
Step2: Analyze each option
Since \( \overline{ER} \) is rotated (a rigid transformation), \( E'R'=ER \). Option (1) \( E'R' = 2ER \) is wrong because rotation does not double the length. Option (2) \( E'R'=\frac{1}{2}ER \) is wrong as rotation does not halve the length. Option (4) \( E'R'=ER + 30 \) is wrong because rotation does not add a constant to the length.
Step1: Property of rotation
In a rotation about a point \( C \), the distance from the center of rotation \( C \) to a pre - image point (e.g., \( H \)) is equal to the distance from \( C \) to its image point (e.g., \( H' \)), and the distance from \( C \) to a pre - image point (e.g., \( I \)) is equal to the distance from \( C \) to its image point (e.g., \( I' \)). Also, the length of a segment \( HI \) is equal to the length of its image segment \( H'I' \).
Step2: Analyze each option
Option (1): The distance from \( C \) to \( I \) (pre - image) and the distance from \( C \) to \( H' \) (image of a different point) do not have to be the same. Option (2): The distance from \( C \) to \( H \) (pre - image) and the distance from \( C \) to \( H' \) (image) are equal (property of rotation). Option (3): The distance from \( H \) to \( I \) (pre - image segment) and the distance from \( H' \) to \( I' \) (image segment) are equal (property of rotation). Option (4): The distance from \( I \) to \( C \) (pre - image) and the distance from \( C \) to \( I' \) (image) are equal (property of rotation).
Step1: Property of rotation
Rotation is a rigid transformation. Rigid transformations preserve the shape and size of a figure, which means that the corresponding angles of the pre - image (\( \triangle MNP \)) and the image (\( \triangle QRS \)) are equal.
Step2: Identify the corresponding angle
In \( \triangle MNP \), \( \angle P=51^{\circ}\), \( \angle M = 59^{\circ}\), \( \angle N=70^{\circ}\). Since \( \triangle QRS\) is the image of \( \triangle MNP\) after rotation, the angles of \( \triangle QRS\) are equal to the angles of \( \triangle MNP\). So \( \angle R\) corresponds to \( \angle P\) (depending on the rotation mapping, but because of congruence of triangles under rotation) and \( \angle R = 51^{\circ}\)
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