Simultaneous equations like 𝒚 = 2𝒙 - 1 and 𝒚 = 𝒙 + 1 can be represented graphically. To solve the equations graphically, the two lines 𝒚 = 𝒙 + 1 and 𝒚 = 2𝒙 - 1 are drawn on the same diagram.

Given any cubic or quartic equation with real coefficients, it can be transformed by a change of variable into a standard form, and thus solved by means of a double-sided scale (Fig. 1) in the case of ...