✔ 最佳答案
x^(1 / 2) + 2[(x / 1)^(-1 / 2)] = 15[(x / 1)^(-3 / 2)]
x^(1 / 2) + 2[(1 / x)^(1 / 2)] = 15[(1 / x)^(3 / 2)]
x^(1 / 2) + 2[1 / x^(1 / 2)] = 15[1 / x^(3 / 2)]
Note: x^(3 / 2) = √(x^3) = √(x * x * x) = √(x^2) * √x = x√x,
as half power equals square root:
√x + (2 / √x) = 15 / (x√x)
Multiply everything by x√x to linearize this, and clear the denominator. By linearize, I just mean put everything on one line.
(√x)(x√x) + (2 / √x)(x√x) = (15 / x√x)(x√x)
Note: (√x)(√x) = √(x * x) = √(x^2) = x
x^2 + 2x = 15
Set equal to zero by subtracting 15 to both sides:
x^2 + 2x - 15 = 0
Factor, as -3 * 5 = -15, and -3 + 5 = 2. Boom!
(x - 3)(x + 5) = 0
Set each quantity equal to zero:
x - 3 = 0, so x = 3
x + 5 = 0, so x = -5
But, we have to dump x = -5 because (-5)^(1 / 2) or √(-5) gives us an imaginary number.
Solution: x = 3
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This is hard because you have rational powers. However, with some manipulation, you can make it a quadratic, which I'm sure you know how to solve.