Solve {l}{x+4y=9}{3x+7u=2}

$$\left\{ \begin{array} { l } { x + 4 y = 9 } \\ { 3 x + 7 u = 2 } \end{array} \right.$$

Solve for x, y

$$x=\frac{2-7u}{3}$$

$$y=\frac{7u+25}{12}$$

Steps Using Substitution

To solve a pair of equations using substitution, first solve one of the equations for one of the variables. Then substitute the result for that variable in the other equation.

$$3x+7u=2,x+4y=9$$

Pick one of the two equations which is more simple to solve for x by isolating x on the left hand side of the equal sign.

$$3x+7u=2$$

Subtract 7u from both sides of the equation.

$$3x=2-7u$$

Divide both sides by 3.

$$x=\frac{2-7u}{3}$$

Substitute \frac{2-7u}{3} for x in the other equation, x+4y=9.

$$\frac{2-7u}{3}+4y=9$$

Subtract \frac{2-7u}{3} from both sides of the equation.

$$4y=\frac{7u+25}{3}$$

Divide both sides by 4.

$$y=\frac{7u+25}{12}$$

The system is now solved.

$$x=\frac{2-7u}{3},y=\frac{7u+25}{12}$$