Answer:
The best option is B: X' = (-7,-4), Y' = (-2,6), Z'=(8, 3).
Step-by-step explanation:
Each vertex can be represented as a vector with regard to origin.
[tex]\vec X = -4\cdot i + 7\cdot j[/tex], [tex]\vec Y = 6\cdot i + 2\cdot j[/tex] and [tex]\vec Z = 3\cdot i -8\cdot j[/tex].
The magnitudes and directions of each vector are, respectively:
X:
[tex]\|\vec X\| = \sqrt{(-4)^{2}+7^{2}}[/tex]
[tex]\|\vec X\| \approx 8.063[/tex]
[tex]\theta_{X} = \tan^{-1}\left(\frac{7}{-4} \right)[/tex]
[tex]\theta_{X} \approx 119.744^{\circ}[/tex]
Y:
[tex]\|\vec Y\| = \sqrt{6^{2}+2^{2}}[/tex]
[tex]\|\vec Y\| \approx 6.325[/tex]
[tex]\theta_{Y} = \tan^{-1}\left(\frac{2}{6} \right)[/tex]
[tex]\theta_{Y} \approx 18.435^{\circ}[/tex]
Z:
[tex]\|\vec Z\| = \sqrt{3^{2}+(-8)^{2}}[/tex]
[tex]\|\vec Z\| \approx 8.544[/tex]
[tex]\theta_{Z} = \tan^{-1}\left(\frac{-8}{3} \right)[/tex]
[tex]\theta_{Z} \approx 290.556^{\circ}[/tex]
Now, the rotation consist is changing the direction of each vector in [tex]\pm 90^{\circ}[/tex], which means the existence of two solutions. That is:
[tex]\vec p = r \cdot [\cos (\theta \pm 90^{\circ})\cdot i + \sin (\theta \pm 90^{\circ})\cdot j][/tex]
Where [tex]r[/tex] and [tex]\theta[/tex] are the magnitude and the original angle of the vector.
Solution I ([tex]+90^{\circ}[/tex])
[tex]\vec p_{X} = 8.063\cdot [\cos (119.744^{\circ}+90^{\circ})\cdot i + \sin (119.744^{\circ}+90^{\circ})\cdot j][/tex]
[tex]\vec p_{X} = -7\cdot i -4\cdot j[/tex]
[tex]\vec p_{Y} = 6.325\cdot [\cos(18.435^{\circ}+90^{\circ})\cdot i+\sin(18.435^{\circ}+90^{\circ})\cdot j][/tex]
[tex]\vec p_{Y} = -2\cdot i +6\cdot j[/tex]
[tex]\vec p_{Z} = 8.544\cdot [\cos(290^{\circ}+90^{\circ})\cdot i +\sin(290^{\circ}+90^{\circ})\cdot j][/tex]
[tex]\vec p_{Z} = 8.029\cdot i +2.922\cdot j[/tex]
Solution II ([tex]-90^{\circ}[/tex])
[tex]\vec p_{X} = 8.063\cdot [\cos (119.744^{\circ}-90^{\circ})\cdot i + \sin (119.744^{\circ}-90^{\circ})\cdot j][/tex]
[tex]\vec p_{X} = 7\cdot i +4\cdot j[/tex]
[tex]\vec p_{Y} = 6.325\cdot [\cos(18.435^{\circ}-90^{\circ})\cdot i+\sin(18.435^{\circ}-90^{\circ})\cdot j][/tex]
[tex]\vec p_{Y} = 2\cdot i -6\cdot j[/tex]
[tex]\vec p_{Z} = 8.544\cdot [\cos(290^{\circ}-90^{\circ})\cdot i +\sin(290^{\circ}-90^{\circ})\cdot j][/tex]
[tex]\vec p_{Z} = -8.029\cdot i -2.922\cdot j[/tex]
The rotated vertices are: i) X' = (-7,-4), Y' = (-2,6), Z'=(8.029, 2.922) or ii) X' = (7,4), Y' = (2,-6), Z' = (-8.029, -2.922). The best option is B: X' = (-7,-4), Y' = (-2,6), Z'=(8, 3).
