answer. Solving simultaneous equations almost always involves combining
equations, but you have to figure out what’s the best way to combine the
equations.
DON’T DO MORE WORK THAN YOU HAVE TO
You don’t always have to find the value of each variable to answer a
simultaneous equations question.You can solve for two variables only if you have two distinct equations. Two
forms of the same equation will not be adequate. Combine the equations in
such a way that one of the variables cancels out. For example, to solve the two
equations 4 x + 3y = 8 and x + y = 3, multiply both sides of the second equation
by –3 to get –3x – 3y = –9. Now add the two equations; the 3y and the –3y
cancel out, leaving x = –1. Plug that back into either one of the original
equations, and you’ll find that y = 4.
Example 9 is a simultaneous equations question.
Example 91. If 2 x – 9y = 11 and x + 12y = –8, what is the value of x + y?(A)