- Calculus, Volume 2: Multi-Variable Calculus and Linear Algebra with Applications to Differential Equations and Probability
- Tom M. Apostol
- Second Edition
- 1991
- 978-1-119-49676-2
2.8 Exercises
In each of Exercises 3 through 12, a function $T: V_2 \rightarrow V_2$ is defined by the formula given for $T(x, y),$ where $(x, y)$ is an arbitrary point in $V_2.$ In each case, determine whether $T$ is one-to-one on $V_2.$ If it is, describe its range $T(V_2);$ for each point $(u, v)$ in $T(V_2),$ let $(x, y) = T^{-1}(u, v)$ and give formulas for determining $x$ and $y$ in terms of $u$ and $v.$
4.$\quad$ $T(x, y) = (x, -y).$
Solution. $\quad$ Let $A = (x_0, y_0)$ and $B = (x_1, y_1)$ be two points in $V_2$ with transformations $T(A) = (x_0, -y_0)$ and $T(B) = (x_1, -y_1).$ Then, if $T(A) = T(B),$ we have $x_0 = x_1$ and $-y_0 = -y_1.$ In other words, if $T(A) = T(B)$ then $A = B.$ Thus, $T$ is a one-to-one transformation on $V_2.$ The range of $T$ is $V_2,$ and for each point $(u, v)$ in $T(V_2),$ we have $x = u$ and $y = -v. \quad \blacksquare$