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Q.Draw the graph of the solution set of the inequations 2x+y≥2, x-y≤1, x+2y≤8, x≥0 and y≥0, also shade the solution region. (Graph paper not necessary)

West Bengal WbchseWest Bengal HS First Year (WBCHSE Class XI) Annual Examination 2018Subjective· 5mImportance★★★★★
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Figure — Draw the first-quadrant feasible region of 2x+y>=2, x-y<=1, x+2y<=8, x>=0, y>=0
Figure — Draw the first-quadrant feasible region of 2x+y>=2, x-y<=1, x+2y<=8, x>=0, y>=0

Locate each boundary line, determine the feasible side (origin test) for each inequation, and find the corner points of the resulting bounded quadrilateral region.

Boundary lines:

L1:2x+y=2L_1: 2x+y=2 (for 2x+y≥22x+y\ge2) — origin gives 0<20<2, so origin is on the infeasible side; feasible region is on the side away from the origin.

L2:x−y=1L_2: x-y=1 (for x−y≤1x-y\le1) — origin gives 0≤10\le1, true, so feasible side contains the origin.

L3:x+2y=8L_3: x+2y=8 (for x+2y≤8x+2y\le8) — origin gives 0≤80\le8, true, so feasible side contains the origin.

Plus x≥0,y≥0x\ge0,y\ge0 restrict to the first quadrant.

Corner points (intersections of boundary lines that satisfy all constraints):

L1∩y-axisL_1\cap y\text{-axis}: x=0⇒y=2x=0\Rightarrow y=2. Point (0,2)(0,2) — check: x−y=−2≤1x-y=-2\le1✓, x+2y=4≤8x+2y=4\le8✓. Valid.

L1∩L2L_1\cap L_2: solving 2x+y=2, x−y=12x+y=2,\ x-y=1 gives x=1,y=0x=1,y=0. Point (1,0)(1,0) — check: x+2y=1≤8x+2y=1\le8✓, x,y≥0x,y\ge0✓. Valid (also lies on the xx-axis).

L2∩L3L_2\cap L_3: solving x−y=1, x+2y=8x-y=1,\ x+2y=8: from x=1+yx=1+y, (1+y)+2y=8⇒y=73, x=103(1+y)+2y=8\Rightarrow y=\dfrac73,\ x=\dfrac{10}3. Point (103,73)\left(\dfrac{10}3,\dfrac73\right) — check 2x+y=9≥22x+y=9\ge2✓. Valid.

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