Wait! There is another solution, as well! Heureka was so close to the second solution, too. I think the user forgot about taking the square root always results in a positive and negative answer. Anyway, I like Heureka's method, but here is my method of solving.
The original equation is \(\sqrt[3]{x^2-4x+4}=16\). Now let's solve for x:
\(\sqrt[3]{x^2-4x+4}=16\) | Raise both sides of the equation to third power to eliminate the cube root. |
\(x^2-2x+4=16^3\) | Do 16^3. luckily for us, we need not know the exact value of it yet. We can manipulate it in a base of 2 so we do not need to do a difficult calculation. |
\(x^2-2x+4=16^3\) | Usually, you would subtract 16^3 on both sides , but \(x^2-2x+4\) happens to be a perfect-square trinomial, and transforming it into one is much easier computationally. |
\((x-2)^2=16^3\) | Take the square root of both sides. Of course, when you take the square root of both sides, it results in a positive and a negative answer. |
\(|x-2|=\sqrt{16^3}\) | Now, I will use power rules creatively to simplify 16^3. |
\(|x-2|=\sqrt{(2^4)^3}\) | 2^4 is equal to 16, so I have not changed the right-hand side of the equation at all. Now, I will utilize another power rule that states that \((a^b)^c=a^{b*c}\) |
\(|x-2|=\sqrt{2^{4*3}}=\sqrt{2^{12}}\) | When you are taking the square root of an even power, just divide the power by 2. Let me show you why. |
\(\sqrt{a^{2k}}=\sqrt{(a^k)^2}=a^k\) | What I have shown here is that any number raised to the power of a number that is a multiple of 2 is simply halved when the square root is taken to it. |
\(\sqrt{2^{12}}=\sqrt{(2^6)^2}=2^6\) | I have done the exact same process as above, just with the numbers that are given. |
\(|x-2|=2^6\) | With absolute value expressions, the answer is divided into the positive and negative answer. Before we do that, however, we must evaluate 2^6. You may have memorized it, but I have a trick if you haven't. |
\(2^6=(2^3)^2=8^2=64\) | Therefore, 2^6=64. |
\(|x-2|=64\) | Now, let's solve for each equation separately. |
\(x-2=64\) | \(-(x-2)=64\) | |
\(x=66\) | \(x-2=-64\) | |
\(x=-62\) | ||
Normally, with equations inside radicals, you would have to check both solutions, but here it isn't necessary. This is because after cubing both sides, you end up with a quadratic, and an answer from a quadratic is always right--assuming no arithmetic error was made when solving. Therefore, your solution set is:
\(x_1=-62\)
\(x_2=66\)
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5x2 | - | 13x | + | 6 | Let's split the middle term. | ||||
Since 5 * 6 = 30 , we need two numbers that add to -13 and multiply to 30 . What two numbers add to -13 and multiply to 30 ? → -10 and -3
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= | 5x2 | - | 10x | - | 3x | + | 6 | Notice if we combine like terms, we get the original expression. | |
Factor 5x out of the first two terms. | |||||||||
= | 5x(x - 2) | - | 3x | + | 6 | ||||
Factor -3 out of the last two terms. | |||||||||
= | 5x(x - 2) | - | 3(x - 2) | ||||||
Factor (x - 2) out of both terms. | |||||||||
= | (x - 2)(5x - 3) |
x|x|=2x+1
The lines are absolute value
\(\begin{array}{|rcll|} \hline x|x| &=& 2x+1 \quad & | \quad \text{square both sides} \\ x^2\cdot |x|^2 &=& (2x+1)^2 \quad & | \quad |x|^2 = x^2 \\ x^2\cdot x^2 &=& (2x+1)^2 \\ x^4 &=& 4x^2+4x+1 \\ \mathbf{x^4 - 4x^2+4x+1} & \mathbf{=} & \mathbf{0} \\ \hline \end{array} \)
solutions of \(x^4 - 4x^2+4x+1 = 0\)
see: http://www.wolframalpha.com/input/?i=x%5E4-4x%5E2-4x-1%3D0
\(\begin{array}{rcll} x_1 &=& -1 \\ x_2 &=& 1 - \sqrt{2} \\ x_3 &=& 1 + \sqrt{2} \\ \end{array}\)
Solutions of \(x|x|=2x+1\):
\(x_1 = -1 \\ \begin{array}{|rcll|} \hline (-1)\cdot |-1| & \overset{?}{=} & 2\cdot (-1)+1 \\ (-1)\cdot 1 & \overset{?}{=} & -2+1 \\ -1 & \overset{!}{=} & -1\ \checkmark \\ \hline \end{array} \)
x = -1 is a solution
\(x_2 = 1 - \sqrt{2} \\ \begin{array}{|rcll|} \hline (1 - \sqrt{2})\cdot |1 - \sqrt{2}| & \overset{?}{=} & 2\cdot (1 - \sqrt{2})+1 \\ (-0.41421356237)\cdot |-0.41421356237| & \overset{?}{=} & 2\cdot (-0.41421356237)+1 \\ (-0.41421356237)\cdot 0.41421356237 & \overset{?}{=} & -0.82842712475 + 1 \\ -0.17157287525 & \ne & 0.17157287525 \\ \hline \end{array}\)
\(\mathbf{x = 1-\sqrt{2} }\) is not a solution
\(x_2 = 1 + \sqrt{2} \\ \begin{array}{|rcll|} \hline (1 + \sqrt{2})\cdot |1 + \sqrt{2}| & \overset{?}{=} & 2\cdot (1 + \sqrt{2})+1 \\ (2.41421356237)\cdot |2.41421356237| & \overset{?}{=} & 2\cdot (2.41421356237)+1 \\ 2.41421356237\cdot 2.41421356237 & \overset{?}{=} & 4.82842712475 + 1 \\ 5.82842712475 & \overset{!}{=} & 5.82842712475\ \checkmark \\ \hline \end{array}\)
\(\mathbf{x = 1+\sqrt{2} }\) is a solution
gray circle area | = | π | * | (radius)2 | ||
radius of the smaller circle = \(\frac{OD}{2}\) | ||||||
gray circle area | = | π | * | (\(\frac{OD}{2}\))2 | ||
gray circle area | = | π | * | \(\frac{OD^2}{4}\) | ||
gray circle area | = | \(\frac{πOD^2}{4}\) |
larger circle area | = | π | * | (radius)2 | ||
radius of the larger circle = OD | ||||||
larger circle area | = | π | * | OD2 |
What, percent, is the gray circle's area out of the larger circle's area?
\(\frac{\text{gray circle area}}{\text{larger circle area}}\,=\,\frac{\frac{\pi OD^2}{4}}{\pi OD^2}\,=\,\frac{\pi OD^2}{4}\,*\,\frac{1}{\pi OD^2}\,=\,\frac14\,=\,\frac{25}{100}\,=\,25\%\)
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