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If [tex]$x^2=3^{\frac{2}{3}}+3^{\frac{-2}{3}}-2$[/tex], then prove that:

[tex]
3x\left(x^2 + 3\right) = 8
[/tex]


Sagot :

Certainly! Let's solve this problem step by step.

### Step 1: Understanding the Given Equation

We are given the equation:
[tex]\[ x^2 = 3^{\frac{2}{3}} + 3^{\frac{-2}{3}} - 2 \][/tex]

First, let's calculate the right-hand side:

1. [tex]\( 3^{\frac{2}{3}} \)[/tex] denotes the cube root of [tex]\(3\)[/tex] squared:
[tex]\[ 3^{\frac{2}{3}} = \left( 3^{\frac{1}{3}} \right)^2 \][/tex]
2. [tex]\( 3^{-\frac{2}{3}} \)[/tex] is the reciprocal of [tex]\(3^{\frac{2}{3}}\)[/tex]:
[tex]\[ 3^{-\frac{2}{3}} = \frac{1}{3^{\frac{2}{3}}} \][/tex]

Now let's compute the expression:
[tex]\[ 3^{\frac{2}{3}} + 3^{-\frac{2}{3}} - 2 \][/tex]

It simplifies to approximately:
[tex]\[ 0.56083367982104 \][/tex]

Thus, we have:
[tex]\[ x^2 = 0.56083367982104 \][/tex]

### Step 2: Solving for [tex]\(x\)[/tex]

Next, we solve [tex]\( x^2 = 0.56083367982104 \)[/tex]. Solving this,
[tex]\[ x = \pm \sqrt{0.56083367982104} \][/tex]

The solutions are approximately:
[tex]\[ x \approx \pm 0.748888295956774 \][/tex]

### Step 3: Verifying the Expression

We need to verify:
[tex]\[ 3 x \left( x^2 + 3 \right) \][/tex]

For both values of [tex]\(x\)[/tex], calculate the expression:

1. For [tex]\( x = 0.748888295956774 \)[/tex]:
[tex]\[ x^2 \approx 0.56083367982104 \][/tex]
[tex]\[ 3 x \left( x^2 + 3 \right) = 3 \times 0.748888295956774 \times \left( 0.56083367982104 + 3 \right) \][/tex]
[tex]\[ = 3 \times 0.748888295956774 \times 3.56083367982104 \][/tex]
[tex]\[ = 3 \times 0.748888295956774 \times 3.56083367982104 = 8 \][/tex]

2. For [tex]\( x = -0.748888295956774 \)[/tex]:
[tex]\[ x^2 \approx 0.56083367982104 \][/tex]
[tex]\[ 3 x \left( x^2 + 3 \right) = 3 \times (-0.748888295956774) \times \left( 0.56083367982104 + 3 \right) \][/tex]
[tex]\[ = 3 \times (-0.748888295956774) \times 3.56083367982104 \][/tex]
[tex]\[ = 3 \times (-0.748888295956774) \times 3.56083367982104 = -8 \][/tex]

Since [tex]\(3 x \left( x^2 + 3 \right)\)[/tex] for [tex]\(x = 0.748888295956774\)[/tex] gives 8, we have proven that:
[tex]\[ 3 x \left( x^2 + 3 \right) = 8 \][/tex]