Step 1: Understand the transformations.
Triangle ABC with vertices A(1,−1), B(3,−1), C(1,3) is mapped to A′B′C′ by transformation T1=(−1001).
Triangle A′B′C′ is then mapped to A′′B′′C′′ by transformation T2=(2021).
a) Find the coordinates of A'B'C'.
To find the coordinates of A′B′C′, we multiply the coordinates of A,B,C by the matrix T1.
For A(1,−1):
A′=(−1001)(1−1)=((−1)(1)+(0)(−1)(0)(1)+(1)(−1))=(−1−1)
So, A′(−1,−1).
For B(3,−1):
B′=(−1001)(3−1)=((−1)(3)+(0)(−1)(0)(3)+(1)(−1))=(−3−1)
So, B′(−3,−1).
For C(1,3):
C′=(−1001)(13)=((−1)(1)+(0)(3)(0)(1)+(1)(3))=(−13)
So, C′(−1,3).
The coordinates of A′B′C′ are A′(−1,−1),B′(−3,−1),C′(−1,3).
b) Find the matrix which maps A'B'C' onto A''B''C''.
The problem statement explicitly gives this matrix as the second transformation.
The matrix is (2021).
c) Determine the area scale factor between A'B'C' and A''B''C''.
The transformation from A′B′C′ to A′′B′′C′′ is given by the matrix T2=(2021).
The area scale factor is the absolute value of the determinant of the transformation matrix.
det(T2)=(2)(1)−(2)(0)=2−0=2
The area scale factor is ∣2∣=2.
d) Find the transformation matrix which maps A''B''C'' onto ABC.
This requires finding the inverse of the combined transformation from ABC to A′′B′′C′′.
First, find the combined transformation matrix Ttotal that maps ABC to A′′B′′C′′. This is T2⋅T1.
Ttotal=T2⋅T1=(2021)(−1001)
Ttotal=((2)(−1)+(2)(0)(0)(−1)+(1)(0)(2)(0)+(2)(1)(0)(0)+(1)(1))
Ttotal=(−2021)
Now, find the inverse of Ttotal. For a matrix M=(acbd), its inverse is M−1=ad−bc1(d−c−ba).
Here, a=−2,b=2,c=0,d=1.
det(Ttotal)=(−2)(1)−(2)(0)=−2−0=−2
Ttotal−1=−21(10−2−2)
Ttotal−1=(−21−20−2−2−2−2)
T_{total}^{-1} = \begin{pmatrix -\frac{1}{2} & 1 \\ 0 & 1 \end{pmatrix}}
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