91Ó°ÊÓ

Determine whether the pair is a solution of the system. $$(1,2),\left\\{\begin{array}{l} x-y=-1 \\ x+y=3 \end{array}\right.$$

Use substitution to solve each system. $$\left\\{\begin{array}{l}y-3 x=9 \\\6x+18=2 y\end{array}\right.$$

Use elimination to solve each system. $$\left\\{\begin{array}{l}\frac{1}{2} x+\frac{4}{7} y=-1 \\\5 x-\frac{4}{5} y=-10\end{array}\right.$$

Use two equations in two variables to solve each application. It takes a motorboat 4 hours to travel 56 miles down a river, and it takes 3 hours longer to make the return trip. Find the speed of the current.

Use substitution to solve each system. $$\left\\{\begin{array}{l}2 x+y=4 \\\4 x+y=5\end{array}\right.$$

Determine whether the pair is a solution of the system. $$(4,1),\left\\{\begin{array}{l} x+y=5 \\ x-y=2 \end{array}\right.$$

Use two equations in two variables to solve each application. A chemist has one solution that is \(40 \%\) alcohol and another that is \(55 \%\) alcohol. How much of each must she use to make 15 liters of a solution that is \(50 \%\) alcohol?

Graph the solution set of each system of inequalities, when possible. SEE EXAMPLE 7. (OBJECTIVE 4) $$\left\\{\begin{array}{l} x \leq 0 \\ y<0 \end{array}\right.$$

Use elimination to solve each system. $$\left\\{\begin{array}{l}5 x=2(y-3) \\\5(x+2)=2 y\end{array}\right.$$

Graph the solution set of each system of inequalities, when possible. SEE EXAMPLE 7. (OBJECTIVE 4) $$\left\\{\begin{array}{l} x<-2 \\ y \geq 3 \end{array}\right.$$