Solving Multi-variable Quadratic Systems

00:00 10 marks

  • Exam Style - Paper 3
  • HL
  • Tier 4
  • Simultaneous equations
  • Quadratic systems
  • Complex solutions

Consider the following two quadratic equations in the variables x and y:

Equation 1: \(x^2 + y^2 – 4x + 2y – 1 = 0\)
Equation 2: \(2x^2 – y^2 + 3x – 5y + 2 = 0\)

(a) Form a system of equations using the equations provided.

(b) Solve the system simultaneously using appropriate methods.

(c) Discuss the possibility of obtaining complex solutions from the system if real intersections do not exist.

Part a

3 minutes 2 marks

Question

Form a system of equations by clearly writing down and simplifying the given quadratic equations: \(x^2 + y^2 – 4x + 2y – 1 = 0\) and \(2x^2 – y^2 + 3x – 5y + 2 = 0\).



Hint Hint

Hint

Start by writing each equation as provided and ensure all terms are correctly grouped.

  • Answer Answer

Complete Answer

The system is:
1) \(x^2 + y^2 – 4x + 2y – 1 = 0\)
2) \(2x^2 – y^2 + 3x – 5y + 2 = 0\)

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Part b

6 minutes 5 marks

Question

Solve the system simultaneously using an appropriate method (such as elimination or substitution). Provide approximate solutions to two decimal places.



Hint Hint

Hint

Consider combining the equations to eliminate one variable or isolating one variable in one equation and substituting into the other.

  • Answer Answer

Complete Answer

The approximate real solutions are \( (x,y) \approx (1.25, 1.49) \) and \( (x,y) \approx (-0.14, 0.40) \).

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Part c

3 minutes 3 marks

Question

Discuss the possibility of obtaining complex solutions from the system if no real intersections were found. Explain graphically what complex solutions represent in the context of these quadratic curves.



Hint Hint

Hint

Examine the discriminant of the derived quadratic equations from the elimination process, or consider the nature of roots of polynomial equations and their graphical interpretation.

  • Answer Answer

Complete Answer

If the discriminant of the quartic equation (or effectively a quadratic equation after elimination of one variable leading to a higher degree polynomial) obtained during the solution process indicates no real roots, then the solutions for \(x\) (and consequently for \(y\)) would be complex. Graphically, real solutions represent intersection points of the curves in the real \(xy\)-plane. Complex solutions, in contrast, imply that the curves do not intersect in the real plane, but would intersect in the complex plane. These complex intersections are not visualizable on a standard real Cartesian plane.

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