[tex]\dfrac{c}{d}+2=\dfrac{f}{g}\ \ \ \ |-2\\\\\dfrac{c}{d}=\dfrac{f}{g}-2\ \ \ \ |\cdot d\\\\c=\dfrac{df}{g}-2d\\\\c=\dfrac{df}{g}-\dfrac{2dg}{g}\\\\c=\dfrac{df-2dg}{g}[/tex]
