Identify which of the following equations represent functions. Select all that apply.

y = 4x + 13
x = 5
x2 + y2 = 16
y2 = One-thirdx - 6
y = 3x2 - x - 1

1 answer

To determine which of the given equations represent functions, we need to check if each equation satisfies the definition of a function. A relation is a function if, for every input (usually x), there is exactly one output (usually y).

  1. y = 4x + 13: This is a linear equation in slope-intercept form (y = mx + b). For every value of x, there is exactly one value of y. This is a function.

  2. x = 5: This is a vertical line where x is always 5. For every y, x will always be 5. There are infinitely many y-values for a single x-value, which means this does not satisfy the function definition. This is not a function.

  3. x^2 + y^2 = 16: This is the equation of a circle centered at the origin with a radius of 4. For most values of x (except at the extremes), there are two corresponding y-values for each x-value. Therefore, this does not represent a function. This is not a function.

  4. y^2 = (1/3)x - 6: This represents a sideways parabola. For certain values of x, there could be two corresponding y-values (positive and negative roots). Thus, this does not meet the definition of a function. This is not a function.

  5. y = 3x^2 - x - 1: This is a quadratic function. For every value of x, there is exactly one corresponding value of y. This is a function.

So, the equations that represent functions are:

  • y = 4x + 13
  • y = 3x^2 - x - 1