0606 P22 - Mar 2025 - Q3 - 4 marks
7197
Solve the equation \(6x^{\frac35}+1=\frac{12}{x^{\frac35}}\), giving your answers correct to 2 decimal places.
Solution
Answer: \(x=1.62\) or \(x=-1.97\).
Work through the given conditions step by step, keeping exact values until the final answer is required.
Let
\(u=x^{\frac35}.\)
Then the equation becomes
\(6u+1=\frac{12}{u}.\)
Multiplying by \(u\),
\(6u^2+u-12=0.\)
Factorise:
\((3u-4)(2u+3)=0.\)
So
\(u=\frac43\quad\text{or}\quad u=-\frac32.\)
Since \(u=x^{3/5}\),
\(x=\left(\frac43\right)^{5/3}=1.62\ldots,\)
or
\(x=-\left(\frac32\right)^{5/3}=-1.97\ldots.\)
Therefore, to 2 decimal places,
\(x=1.62\quad\text{or}\quad x=-1.97.\)
This gives the required answer: \(x=1.62\) or \(x=-1.97\).