1. **Problem statement:** We have a 12-inch by 16-inch piece of cardboard. We cut out squares of side length $x$ from each corner and fold up the sides to form an open box. We want to find the value of $x$ that maximizes the volume of the box and then find the dimensions of the box.
2. **Formula for volume:** The volume $V$ of the box is given by the area of the base times the height. After cutting out squares of side $x$, the base dimensions become $(16 - 2x)$ by $(12 - 2x)$, and the height is $x$. So,
$$V = x(16 - 2x)(12 - 2x)$$
3. **Simplify the volume expression:**
$$V = x(192 - 32x - 24x + 4x^2) = x(192 - 56x + 4x^2) = 192x - 56x^2 + 4x^3$$
4. **Find critical points:** To maximize volume, find $V'$ and set it to zero.
$$V' = 192 - 112x + 12x^2$$
Set $V' = 0$:
$$12x^2 - 112x + 192 = 0$$
Divide by 4:
$$3x^2 - 28x + 48 = 0$$
5. **Solve quadratic:**
$$x = \frac{28 \pm \sqrt{28^2 - 4 \cdot 3 \cdot 48}}{2 \cdot 3} = \frac{28 \pm \sqrt{784 - 576}}{6} = \frac{28 \pm \sqrt{208}}{6}$$
$$\sqrt{208} = 4\sqrt{13} \approx 14.42$$
So,
$$x_1 = \frac{28 + 14.42}{6} \approx 7.07, \quad x_2 = \frac{28 - 14.42}{6} \approx 2.60$$
6. **Check domain:** Since $x$ must be less than half the smaller side (6 inches), $x=7.07$ is invalid. So $x \approx 2.60$ inches.
7. **Calculate dimensions:**
Bottom length = $16 - 2x = 16 - 2(2.60) = 16 - 5.2 = 10.8$ inches
Bottom width = $12 - 2x = 12 - 5.2 = 6.8$ inches
Height = $x = 2.60$ inches
**Final answer:**
Dimensions of the bottom: $10.8$ inches by $6.8$ inches
Height of the box: $2.6$ inches
Max Volume Box
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