## Elementary Technical Mathematics

The two lines/equations $coincide$ (overlap). Infinite solutions.
We use the addition method: We add the 2 equations: $3x-5y=7$ $9x-15y=21$ Multiply both sides of the first equation by $-3$ to cancel $x$. $-9x+15y=-21$ $\underline{+9x-15y=+21}$ $0=0$ This is a true statement, which means that we have infinite solutions. So, the two equations coincide (overlap).