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Algebra Difficulty 4.9 AIME Find the answer

6.060. 5x+735x123=1\sqrt[3]{5 x+7}-\sqrt[3]{5 x-12}=1.

Solve the equation 5x+735x123=1\sqrt[3]{5 x+7}-\sqrt[3]{5 x-12}=1.

A number or a short expression. Spacing and $ signs are ignored.

Solution

## Solution.

Let's rewrite the equation as 5x+73=5x123+1\sqrt[3]{5 x+7}=\sqrt[3]{5 x-12}+1 and cube both sides:

5x+7=5x12+3(5x123)2+35x123+1(5x123)2+5x1236=0 \begin{aligned} & 5 x+7=5 x-12+3(\sqrt[3]{5 x-12})^{2}+3 \sqrt[3]{5 x-12}+1 \Leftrightarrow \\ & \Leftrightarrow(\sqrt[3]{5 x-12})^{2}+\sqrt[3]{5 x-12}-6=0 \end{aligned}

Let 5x123=t\sqrt[3]{5 x-12}=t. The equation in terms of tt becomes t2t6=0t^{2}-t-6=0, from which we find t1=3t_{1}=-3 and t2=2t_{2}=2.

Then either 5x123=3,5x12=27,x1=3\sqrt[3]{5 x-12}=-3, 5 x-12=-27, x_{1}=-3, or 5x123=2\sqrt[3]{5 x-12}=2, 5x12=8,x2=45 x-12=8, x_{2}=4.

Answer: x1=3,x2=4x_{1}=-3, x_{2}=4.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.