Math Problem Statement

Two numbers add to 6. Let V denote the sum of the first number and the square of twice the second number. What is the smallest possible value for V?

Solution

Let's denote the two numbers as xx and yy. We are given:

x+y=6x + y = 6

We want to minimize VV, which is defined as:

V=x+(2y)2V = x + (2y)^2

First, simplify the expression for VV:

V=x+4y2V = x + 4y^2

Since x+y=6x + y = 6, we can express xx in terms of yy:

x=6yx = 6 - y

Substitute this into the expression for VV:

V=(6y)+4y2V = (6 - y) + 4y^2

Simplifying, we get:

V=6y+4y2V = 6 - y + 4y^2

To find the minimum value of VV, we'll take the derivative of VV with respect to yy and set it equal to zero:

dVdy=1+8y\frac{dV}{dy} = -1 + 8y

Setting the derivative equal to zero:

1+8y=0-1 + 8y = 0

Solving for yy:

8y=1y=188y = 1 \quad \Rightarrow \quad y = \frac{1}{8}

Next, substitute y=18y = \frac{1}{8} back into the expression for VV to find the minimum value:

V=618+4(18)2V = 6 - \frac{1}{8} + 4\left(\frac{1}{8}\right)^2

Simplify this expression:

V=618+4×164V = 6 - \frac{1}{8} + 4 \times \frac{1}{64}

V=618+116V = 6 - \frac{1}{8} + \frac{1}{16}

V=6216+116=6116V = 6 - \frac{2}{16} + \frac{1}{16} = 6 - \frac{1}{16}

V=9616116=9516=5.9375V = \frac{96}{16} - \frac{1}{16} = \frac{95}{16} = 5.9375

So, the smallest possible value for VV is 5.9375\boxed{5.9375}.

Would you like any more details or have any questions?

Here are some related questions:

  1. How does changing the coefficient of y2y^2 affect the minimum value of VV?
  2. What does the second derivative tell us about the nature of the minimum?
  3. How would the problem change if the numbers added to a different sum instead of 6?
  4. Can you find a maximum value for VV given these constraints?
  5. How can this method be extended to minimize other similar expressions?

Tip: When dealing with quadratic functions, the minimum or maximum value can often be found efficiently by taking the derivative and solving for critical points.

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations

Formulas

Quadratic equation formula ax^2 + bx + c = 0

Theorems

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Suitable Grade Level

Grades 10-12