How do you determine whether a linear system has one solution, many solutions, or no solution when given 2x+3y= -12 and 2x-y = -4?

1 Answer
Nov 6, 2015

If the gradients are different in a 2 equation linear system then 1 solution

If they are parallel then no solution. They will not cross.

Explanation:

In your case it is given that:
2x+3y=12..................................(1)
2xy=4.......................................(2)

Write as:

y=23x4...........................(1a)
y=2x+4....................................(2a)

The gradient of (1a) is negative so its plot has a downward slope when progressing from left to right.

The gradient of (2a) is positive so its plot has an upward slope as you progress from left to right.

As there is no restraint on the magnitude of x we have x so at some point they will cross and then carry on. This will produce just 1 solution.