Algebra · real student question

Solve the system x² + y = 2 and −x² + y = 10.

Question

Solve the system

{x2+y=2x2+y=10\begin{cases}x^{2}+y=2\\-x^{2}+y=10\end{cases}

Step-by-step solution

  1. Spot the elimination that the system is built for. The two equations contain +x2+x^{2} and x2-x^{2}, so simply adding them removes xx entirely — no substitution or squaring is needed.

  2. Add the equations.

    (x2+y)+(x2+y)=2+102y=12y=6(x^{2}+y)+(-x^{2}+y)=2+10\quad\Longrightarrow\quad 2y=12\quad\Longrightarrow\quad y=6

  3. Substitute y = 6 back into either equation. Using the first:

    x2+6=2x2=4x^{2}+6=2\quad\Longrightarrow\quad x^{2}=-4

  4. Interpret the impossible equation. The square of any real number is 0\ge 0, so x2=4x^{2}=-4 has no real solution. Since yy was forced to be 66, there is no real pair (x,y)(x,y) satisfying both equations.

    No real solution\boxed{\text{No real solution}}

  5. Confirm with the second equation and with geometry. Substituting y=6y=6 into x2+y=10-x^{2}+y=10 gives x2=4-x^{2}=4, i.e. x2=4x^{2}=-4 again — the same contradiction, so no algebraic slip occurred. Geometrically, y=2x2y=2-x^{2} is a downward parabola with vertex (0,2)(0,2) and y=10+x2y=10+x^{2} is an upward parabola with vertex (0,10)(0,10); the first never rises above y=2y=2 and the second never falls below y=10y=10, so their graphs cannot meet.

  6. Note the complex solutions, if the problem allows them. Over the complex numbers x2=4x^{2}=-4 gives x=±2ix=\pm 2i, so the pairs (2i,6)(2i,6) and (2i,6)(-2i,6) satisfy both equations. Answer choices such as (4,14)(4,-14), (4,14)(-4,-14) or (0,2)(0,2) do not satisfy either equation and can be rejected by direct substitution.

Answer

No real solution (over C: (±2i,6))\text{No real solution (over }\mathbb{C}:\ (\pm 2i,\,6))

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