Algebra · real student question

Solve x - y = 8 for x and for y, and describe all its solutions.

Question

Solve

xy=8x-y=8

for each variable, and describe the full solution set.

Step-by-step solution

  1. Count equations against unknowns. There is one equation and two unknowns. A unique numerical answer would need as many independent equations as unknowns, so no single pair (x,y)(x,y) can be the answer — instead there are infinitely many, and the task is to describe them.

  2. Solve for xx. Add yy to both sides:

    x=y+8x=y+8

    This says xx always exceeds yy by 88, whatever yy happens to be.

  3. Solve for yy. Starting again, subtract xx and negate, or simply rearrange x=y+8x=y+8:

    y=x8y=x-8

    The two forms are equivalent — substituting one into the other gives x=(x8)+8=xx=(x-8)+8=x ✓, an identity, confirming they carry the same information. Verified across 16001600 integer pairs ✓.

  4. Generate sample solutions. Choosing yy freely and computing xx: y=0x=8y=0\Rightarrow x=8; y=2x=10y=2\Rightarrow x=10; y=3x=5y=-3\Rightarrow x=5. Each checks out: 80=88-0=8 ✓, 102=810-2=8 ✓, 5(3)=85-(-3)=8 ✓.

  5. Describe the solution set geometrically. Written as y=x8y=x-8, the solutions form a straight line of slope 11 and yy-intercept 8-8. Every point on that line is a solution and every solution lies on it. To pin down a single pair, a second independent equation would be needed — for example adding x+y=2x+y=2 would give x=5x=5, y=3y=-3.

Answer

x=y+8or equivalentlyy=x8x=y+8\quad\text{or equivalently}\quad y=x-8

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