Mathematics
Points (4, 0) and (-3, 0) are invariant points under reflection in line L1; points (0, 5) and (0, -2) are invariant under reflection in line L2.
(i) Name and write the equations of lines L1 and L2.
(ii) Write P', the reflection of P(6, -8) in L1 and P" the image of P in L2.
(iii) State a single transformation that maps P' onto P".
Reflection
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Answer
We know that,
y-coordinate of points lying on x-axis is zero and x-coordinate of points lying on y-axis is zero.
∴ (4, 0) and (-3, 0) lies on x-axis and (0, 5) and (0, -2) lies on y-axis.
Also,
A point is invariant under reflection in the line on which it lies itself.
Given,
(4, 0) and (-3, 0) are invariant points under reflection in line L1.
(i) Since, (4, 0) and (-3, 0) lies on x-axis so they are invariant under reflection in x-axis.
∴ L1 = x-axis
(0, 5) and (0, -2) are invariant points under reflection in line L2.
Since, (0, 5) and (0, -2) lies on y-axis so they are invariant under reflection in y-axis.
∴ L2 = y-axis
Hence, L1(x-axis) : y = 0 and L2(y-axis) : x = 0.
(ii) We know that,
On reflection in x-axis, the sign of y-coordinate changes.
∴ P(6, -8) on reflection in L1 becomes P'(6, 8).
On reflection in y-axis, the sign of x-coordinate changes.
∴ P(6, -8) on reflection in L2 becomes P"(-6, -8).
Hence, coordinates of P' = (6, 8) and P" = (-6, -8).
(iii) We know that,
On reflection in origin, the sign of both x-coordinate and y-coordinate changes.
∴ P'(6, 8) on reflection in origin, becomes P"(-6, -8).
Hence, single transformation that maps P' onto P" is reflection in origin.
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