Question

 Determine whether the system of linear equations has one and only one solution, infinitely many solutions, or no solution. Find all solutions whenever they exist.
X + 3y = 9
 

3x –y =  7

Answer 1

$After\ adding\ equations\ and\ simplifying:\\\\One\ solution:\\\\x=number\\ example: x=2\\\\ infinitely\ many\ solutions:\\\\ Left\ side=\ Right\ side\\ example:\\ 2=2\\\\ No\ solutions:\\\\2 \neq 5$$\left \{ {{x+3y=9} \atop {3x-y=7}\ \ |*3} \right.\\\\ \left \{ {{x+3y=9} \atop {9x-3y=21}} \right.\\+--------\\\\Addition\ method:\\\\10x=30\ \ |:10 \\\\x=3\\\\x+3y=9\\\\3y =9-x=9-3=6\\\\y=2\\\\ \left \{ {{y=2} \atop {x=3}} \right.$