What substitution should be used to rewrite x to the 8th power minus 3 x to the 4th power plus 2 is equal to 0 as a quadratic equation?
Answer
A
u is equal to x to the 8th power
B
u is equal to x to the 4th power
C
u is equal to x to the 16th power
D
u is equal to x squared
Explanation
Let u = x⁴. Then x⁸ = (x⁴)² = u², so the equation becomes u² − 3u + 2 = 0, which is quadratic in u. Therefore, the correct choice is “u is equal to x to the 4th power.”
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