# Combined Transformation

Find the coordinates of the image of a point A(3, -5) after reflection on the line x + y = 0 followed by the rotation through +90° about the origin.

A(3, -5) $\ce{->[x \, = \, -y]}$ A'(5, -3)

Again, A" be the final image when point A' is rotated through +90° about the origin,

A'(5, -3) $\ce{->[+90°]}$ A"(3, 5)

Find the coordinates of the image of a point (4, 7) when it is first rotated about the origin through -90° and then the image so formed is translated by $\begin{pmatrix} 3 \\ 4 \end{pmatrix}$

A(4, 7) $\ce{->[+90°]}$ A'(7, -4)

Again, A" be the final image when point A' is translated by
$\begin{pmatrix}
3 \\
4
\end{pmatrix}$,

A'(7, -4) $\ce{->[T.V. \begin{pmatrix}
3 \\
4
\end{pmatrix}]}$ A"(7 + 3, -4 + 4) = A"(10, 0)

The point P(2, -3) is reflected on the X-axis. The image P" thus obtained is rotated through +90° about origin. Find the co-ordinates of the final image P" and P'.

P(2, -3) $\ce{->[x-axis]}$ P'(2, 3)

Again, P" be the final image when point P' is rotated through +90°
about origin,

P'(2, 3) $\ce{->[+90°]}$ P"(-3, 2)

Reflect the point P(3, 4) on the y-axis. Rotate the image so obtained about the origin and through 90° in positive direction about the origin and find its final image.

P(3, 4) $\ce{->[y-axis]}$ P'(-3, 4)

Again, P" be the final image when point P' is rotated through 90°
in the positive direction.

P'(-3, 4) $\ce{->[+90°]}$ P"(-4, -3)

Point P(-2,3) is first reflected on y-axis and the image so obtained is rotated through -90° about the origin. Find the coordinate of the image formed after the rotation.

P(-2, 3) $\ce{->[y-axis]}$ P'(2, 3)

Again, P" be the final image after rotating P' through -90° about
the origin.

P'(2, 3) $\ce{->[-90°]}$ P"(3, -2)

Point A(2, 5) is first reflected on X-axis. The image so obtained is rotated through 90° in positive direction about origin. Find the final image of A(2,5).

A(2, 5) $\ce{->[x-axis]}$ A'(2, -5)

Again, A" be the final image when point A' is rotated through 90°
in positive direction about origin.

A'(2, -5) $\ce{->[+90°]}$ A"(5, 2)

If r_{1} is the reflection on y-axis and r_{2} is the
reflection on the line y - 5 = 0, then find the image of point (5, 3)
under the combined transformation r_{1}∘r_{2}.

_{1}∘r

_{2}. r

_{2}is followed by r

_{1}.

r

_{2}is the reflection on y - 5 = 0, so,

A(x, y) $\ce{->[r_2][\text{y = 5}]}$ A'(x, 10 - y)

r_{1} is the reflection on y-axis. so,

A'(x, 10 - y) $\ce{->[r_1][y-axis]}$ A"(-x, 10 - y)

Finally,

A(x, y) $\xrightarrow{r_1 \circ r_2}$ A"(-x, 10 - y)

P" be the final image of point P(5, 3) under the given combination,
then,

P(5, 3) $\xrightarrow{r_1 \circ r_2}$ P"(-5, 7)

Reflect point P(5, 6) on the line x = 2. Enlarge the image so obtained by E[(0,0), 2]. Write the coordinates of the image.

P(5, 6) $\xrightarrow{\text{x = 2}}$ P'(2 × 2 - 5, 6), P'(-1, 6)

Also, P" be the final image obtained when P' is enlarged by E[(0,0) ,2],

P'(-1, 6) $\xrightarrow{\text{E[(0,0) ,2]}}$ P"(-1 × 2, 6
× 2), P"(-2, 12)

Hence, the coordinate of the images are P'(-1, 6) and P"(-2, 12).

Reflect point A(4, 5) on the line y = 2. Enlarge the image so obtained by E[(0,0),2]. Write the coordinate of the image.

A(4, 5) $\xrightarrow{\text{y = 2}}$ A'(4, 4 - 5), A'(4, -1)

Also, A" be the final image obtained by enlargement of A' on E[(0, 0), 2],

A'(4, -1) $\xrightarrow{\text{E[(0, 0), 2]}}$ A"(8, -2)

If r_{1} is the reflection about the X-axis and r_{2} is
the rotation about +90° through the origin, find the image of the point
A(3, -6) under the combined transformation of
r_{1}∘r_{2}.

_{1}∘r

_{2}. r

_{2}is followed by r

_{1}.

r

_{2}is the rotation about +90° through origin, so,

A(x, y) $\ce{->[r_2][+90°]}$ A'(-y, x)

r_{1} is the reflection on x-axis. so,

A'(-y, x) $\ce{->[r_1][x-axis]}$ A"(-y, -x)

Finally,

A(x, y) $\xrightarrow{r_1 \circ r_2}$ A"(-y, -x)

P" be the final image of point P(3, -6) under the given combination,
then,

P(3, -6) $\xrightarrow{r_1 \circ r_2}$ P"(6, -3)

T denotes a translation vector $(\frac23 )$ and R denotes the reflection in the line y = 3. If R∘T (a, 3) = (5, b), find the values of a and b.

T denotes a translation vector $(\frac23 )$, so,

T(a, 3) $\xrightarrow{\text{T.V.}(\frac 23)}$ T'(a + 2, 6)

From above,

R∘T(a , 3) = R(a + 2, 6)

R denotes the reflection
in the line y = 3. so,

R(a + 2, 6) $\xrightarrow{\text{y = 3}}$ R'(a + 2, 0)

So, R∘T(a , 3) = (a + 2, 0)

Hence, by comparing it with (i), we get, `a` = 3 and `b` = 0.

Point (4, -3) is reflected in the line x = 0 at first and then the image so formed is reflected in the line y = k so that the final image (-4, 9) is obtained. Find the value of k.

A(4, -3) $\xrightarrow{\text{x = 0}}$ A'(-4, -3)

Also, A" be the final image formed by reflecting A' in the line y = k.
so,

A'(-4, -3) $\xrightarrow{\text{y = k}}$ A"(-4, 2k + 3)

We have given, A"(-4, 9)

Comparing the coordinates of A", we get, 2k + 3 = 9, so, k = 3.

If r_{1} represents the reflection about x-axis and r_{2}
represents the rotation about the origin through +90°, find the image
point of the point N(-3, 2) under the combined transformation of
r_{1}∘r_{2}.

_{1}∘r

_{2}. r

_{2}is followed by r

_{1}.

r

_{2}is the rotation about +90° through origin, so,

A(x, y) $\ce{->[r_2][+90°]}$ A'(-y, x)

r_{1} is the reflection on x-axis. so,

A'(-y, x) $\ce{->[r_1][x-axis]}$ A"(-y, -x)

Finally,

A(x, y) $\xrightarrow{r_1 \circ r_2}$ A"(-y, -x)

P" be the final image of point P(-3, 2) under the given combination,
then,

P(-3, 2) $\xrightarrow{r_1 \circ r_2}$ P"(-2, 3)

R_{1} and R_{2} denote the reflection in the line y = 2
and line x = -y respectively. Which point has the image A'(-3, 2) under
the combined transformation R_{1}∘R_{2}? Find it.

_{1}∘R

_{2}. R

_{2}is followed by R

_{1}.

R

_{2}is the reflection in the line x = -y, so,

P(x, y) $\ce{->[R_2][\text{x = -y}]}$ P'(-y, -x)

R_{1} is the reflection in the line y = 2. so,

P'(-y, -x) $\ce{->[R_1][\text{y = 2}]}$ P"(-y, 4 + x)

Finally,

P(x, y) $\xrightarrow{R_1 \circ R_2}$ P"(-y, -x) --- (I)

Let the point A(a, b) has the image A'(-3, 2) under the given
combination, then,

A(a, b) $\xrightarrow{R_1 \circ R_2}$ A'(-3, 2) --- (II)

Comparing the value of `a` and `b` by the help of
(I) and (II), we get, `a` = -2 and `b` = 3

Find the co-ordinates of the point A whose image after reflection about the line y = x, followed by the reflection about the line y = 0 is A"(6, -5).

A(x, y) $\xrightarrow{\text{y = x}}$ A'(y, x)

Again, A" be the image formed when A' is reflected about the line y = 0.

A'(y, x) $\xrightarrow{\text{y = 0}}$ A"(y, -x)

So, from above,

A(x, y) $\rightarrow$ A"(y, -x)

We have given, A"(6, -5). So, comparing A"(y, -x) and A"(6, -5), we get,

`x` = 5 and `y` = 6.