3.3 Lösning 3b

\[\begin{array}{rclcl} x \, + \, (x \, + \, 6) & = & 12 & & \\ x \, + \, x \, + \, 6 & = & 12 & & \\ 2\,x \, + \, 6 & = & 12 & \qquad | & - \, 6 \\ 2\,x \, + \, 6 \, - \, 6 & = & 12 \, - \, 6 & & \\ 2\,x \, & = & 6 & \qquad | & / \; 2 \\ \displaystyle \frac{2\,x}{2} & = & \displaystyle \frac{6}{2} & & \\ x \, & = & 3 & & \end{array}\]

Kontroll:

\( \, x = 3 \quad \) insatt i \( \quad x \, + \, (x \, + \, 6) \, = \, 12 \, \):

VL \( \, = \, 3 \, + \, (3 \, + \, 6) \, = \, 3 \, + \, 3 \, + \, 6 \, = \, 12 \)

HL \( \, = \, 12 \)

VL \( \; = \; \) HL \( \quad \Longrightarrow \quad \) OK