Algebra · real student question

Graph the system of inequalities x + y ≤ 6 and x ≥ 2, and describe the solution region.

Question

Graph the system

x+y6,x2,x+y\le 6,\qquad x\ge 2,

and describe the resulting solution region.

Step-by-step solution

  1. Rewrite the first inequality with yy isolated. Subtracting xx,

    y6x.y\le 6-x.

    Putting it in "yy\le" form tells you immediately which side of the boundary line to shade: below it, not above.

  2. Draw the two boundary lines. The boundary of the first is y=6xy=6-x, a line of slope 1-1 through (0,6)(0,6) and (6,0)(6,0). The boundary of the second is the vertical line x=2x=2. Both inequalities are non-strict (\le, \ge), so both lines are drawn solid and belong to the solution.

  3. Shade each region and take the overlap. For y6xy\le 6-x, shade everything on or below the slanted line; for x2x\ge 2, shade everything on or to the right of x=2x=2. The solution set is the intersection of the two shaded half-planes.

  4. Locate the corner. The two boundaries meet where x=2x=2 and y=62=4y=6-2=4, so the vertex of the region is (2,4)(2,4). From there the region opens downward and to the right — it is unbounded, since nothing prevents xx or y-y from growing.

  5. Write the region and test points. The solution is

    {(x,y)  :  x2 and y6x}.\{(x,y)\;:\;x\ge 2\ \text{and}\ y\le 6-x\}.

    Check (3,1)(3,1): 323\ge2 ✓ and 3+1=463+1=4\le6 ✓, so it is in the region. Check (1,1)(1,1): 121\ge2 fails, so it is out. Check (4,3)(4,3): 424\ge2 ✓ but 4+3=7>64+3=7>6, so it is out. The corner (2,4)(2,4) itself satisfies both with equality and is included.

Answer

{(x,y):x2,  y6x}, an unbounded region with corner (2,4)\{(x,y):x\ge 2,\;y\le 6-x\},\ \text{an unbounded region with corner }(2,4)

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