Ex [1] If 2x + y = 5 and 3x + 2y = 9, then x = ___.
a. In this problem, the 1st equation has a single 'y' so we can solve for
y and get y = 5 - 2x. Now we can substitute this value into the 2 nd
equation.
b. Doing so gives 3x + 2(5 - 2x) = 9. Now we have an equation with