What's the answer (X) in equation below:

[(22.44*(X^-1.5))+(16.8*(X^-.05))]=1.875
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1 Answer

22.44x⁻¹˙⁵+16.8x⁻⁰˙⁰⁵=1.875.

When x=1, the left-hand side becomes 39.24.

Let x=10¹⁰ the left-hand side becomes:

22.44×10⁻¹⁵+1.68√10=5.313 approx. So the left-hand side decreases as x increases. The first term becomes insignificant as x increases. When x=10²⁰, we have:

22.44×10⁻³⁰+1.68=1.68 approx. Therefore the solution is between x=10 and 20.

An approximation for the solution is 16.8x⁻⁰˙⁰⁵=1.875.

x⁻⁰˙⁰⁵=0.1116 approx, -0.05log(x)=log(0.1116),

log(x)=19.0462, x=1.1121×10¹⁹.

This is probably not the answer intended so I suggest the equation should have been:

22.44x⁻¹˙⁵+16.8x⁻⁰˙⁵=1.875,

22.44+16.8x=1.875x¹˙⁵,

(22.44+16.8x)²=1.875²x³,

1.875²x³-16.8²x²-2(22.44)(16.8x)-22.44²=0.

For convenience, let a=1.875, b=16.8, c=22.44:

a²x³-b²x²-2bcx-c²=0.

We can use Newton’s Method to solve this cubic.

First, differentiate: 3a²x²-2b²x-2bc

x=x-(a²x³-b²x²-2bcx-c²)/(3a²x²-2b²x-2bc) is the iterative equation.

Graphically, the only real solution is near x=80, so we use this to start the iterative process:

x₀=80,

x₁=83.11096295,

x₂=82.89096876,

x₃=82.88981613,

x₄=82.8898161,

x₅=82.8898161017.

Reduce this to 4 decimal places: x=82.8898.

by Top Rated User (1.2m points)

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