Question

Difficulty: MediumSimultaneous Linear and Quadratic Equations

What are the values of yy that satisfy the simultaneous equations 3x+y=103x + y = 10 and x2+y=14x^2 + y = 14?

  1. A
    1-1 or 44
  2. B
    13-13 or 22
  3. 2-2 or 1313Answer
  4. D
    77 or 2222

Answer

The values of yy that satisfy the simultaneous equations are 2-2 or 1313.
Rearranging the linear equation gives y=103xy = 10 - 3x. Substituting this into x2+y=14x^2 + y = 14 yields x2+103x=14x^2 + 10 - 3x = 14, which simplifies to x23x4=0x^2 - 3x - 4 = 0. Factoring gives (x4)(x+1)=0(x - 4)(x + 1) = 0, so x=4x = 4 or x=1x = -1. Substituting x=4x = 4 into y=103xy = 10 - 3x gives y=2y = -2, and substituting x=1x = -1 gives y=13y = 13. Thus, the required values of yy are 2-2 or 1313.

Step-by-Step Solution

1
Express yy in terms of xx from the linear equation
y=103xy = 10 - 3x
Isolation of variable yy allows straightforward substitution into the quadratic equation.
2
Substitute y=103xy = 10 - 3x into the quadratic equation x2+y=14x^2 + y = 14
x2+(103x)=14    x23x4=0x^2 + (10 - 3x) = 14 \implies x^2 - 3x - 4 = 0
Creates a quadratic equation in terms of a single variable xx.
3
Solve the quadratic equation x23x4=0x^2 - 3x - 4 = 0 for xx
(x4)(x+1)=0    x=4 or x=1(x - 4)(x + 1) = 0 \implies x = 4 \text{ or } x = -1
Factoring determines the xx-coordinates of the solution points.
4
Substitute each xx-value back into y=103xy = 10 - 3x to find the corresponding yy-values
For x=4x = 4: y=103(4)=2y = 10 - 3(4) = -2; for x=1x = -1: y=103(1)=13y = 10 - 3(-1) = 13
Evaluates the exact values of yy requested by the question.

Key Concept

Simultaneous Linear and Quadratic Equations
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