Simultaneous Equations - A-Level Maths by StudyWell
Solve the simultaneous equations
This example requires solution via substitution, i.e. make either x or y the subject of one equation and insert it into the other. The obvious choice would be to make x the subject of the second equation – it is the quickest, least complicated choice. The second equation tells us that . We can insert this into the first equation: . By multiplying out the brackets and simplifying we see that this is a quadratic equation in y:
This tells us that y has to be either 3 or 1. If , then (from the second equation) and if then .