Verified Answer :

  • To convert \(y = x^2 + 8x - 3\) into vertex form, identify the coefficient of \(x\), which is 8.
  • Take half of this coefficient (4) and square it (16) to complete the square: \(x^2 + 8x + 16 - 16 - 3\).
  • Factor the expression as a perfect square: \((x+4)^2 - 19\).
  • The final vertex form is \(y = (x + \boxed{4})^2 + \boxed{-19}\).

Explanation

  1. Understanding the Problem

The problem asks to rewrite the quadratic function \(y = x^2 + 8x - 3\) in the vertex form \(y = (x + h)^2 + k\). The standard form of a quadratic function is \(y = ax^2 + bx + c\). In our case, \(a = 1\), \(b = 8\), and \(c = -3\). To convert this to vertex form, we use a method known as completing the square. The vertex form \(y = a(x - h)^2 + k\) allows us to easily identify the vertex of the parabola, \((h, k)\).

  1. Completing the Square

To complete the square, we focus on the first two terms: \(x^2 + 8x\). We want to add a constant to these terms to form a perfect square trinomial of the form \(x^2 + bx + (\frac{b}{2})^2 = (x + \frac{b}{2})^2\). Here, the coefficient of \(x\) is \(8\). We take half of this coefficient, which is \(\frac{8}{2} = 4\), and then square it to get \(4^2 = 16\). To keep the expression equivalent to the original one, we add and subtract this value:
\[x^2 + 8x - 3 = (x^2 + 8x + 16) - 16 - 3\]

  1. Finalizing the Vertex Form

Now, we factor the perfect square trinomial \((x^2 + 8x + 16)\) into \((x + 4)^2\). Substituting this back into our expression, we get:
\[(x^2 + 8x + 16) - 16 - 3 = (x + 4)^2 - 19\]
Thus, the function in vertex form is \(y = (x + 4)^2 - 19\). Comparing this to the desired form \(y = (x + \boxed{\phantom{0}})^2 + \boxed{\phantom{0}}\), we identify the missing values as \(4\) and \(-19\).

Examples

The vertex form is incredibly useful in real-world scenarios such as projectile motion. For example, if a ball is thrown into the air, its height over time is often modeled by a quadratic function. By rewriting this function in vertex form, we can immediately identify the maximum height the ball reaches (the \(k\) value) and the time at which it happens (the \(h\) value). Understanding how to convert between forms allows us to quickly analyze the peak of a trajectory, making physics and engineering problems much simpler to solve!