What substitution should be used to rewrite 4 x to the 12th power minus 5 x to the 6th power minus 14 is equal to 0 as a quadratic equation?

The equation contains both x to the 12th power and x to the 6th power. Since x to the 12th power is (x to the 6th power) squared, let u = x to the 6th power; then the equation becomes 4u² − 5u − 14 = 0, a quadratic equation. The correct choice is D, u = x to the 6th power.

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