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Alborosie
3 years ago
14

If 1/x + 1/3x equals 4 then what is x

Mathematics
1 answer:
Vikki [24]3 years ago
3 0

Answer:

\huge\boxed{x=\dfrac{1}{3}}

Step-by-step explanation:

\dfrac{1}{x}+\dfrac{1}{3x}=4\\\\\text{Domain:}\ x\neq0\\\\\text{find LCD}=3x\\\\\dfrac{1\cdot3}{x\cdot3}+\dfrac{1}{3x}=4\\\\\dfrac{3}{3x}+\dfrac{1}{3x}=4\\\\\dfrac{3+1}{3x}=4\\\\\dfrac{4}{3x}=\dfrac{4}{1}\qquad\text{cross multiply}\\\\(3x)(4)=(4)(1)\\\\12x=4\qquad\text{divide both sides by 12}\\\\\dfrac{12x}{12}=\dfrac{4}{12}\\\\x=\dfrac{4:4}{12:4}\\\\x=\dfrac{1}{3}\in D

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dsp73

Looks like f(x,y)=x^2+y^2-x^2y+7.

f_x=2x-2xy=0\implies2x(1-y)=0\implies x=0\text{ or }y=1

f_y=2y-x^2=0\implies2y=x^2

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The latter two critical points occur outside of D since |\pm\sqrt2|>1 so we ignore those points.

The Hessian matrix for this function is

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Now consider each boundary:

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f(1,y)=8-y+y^2=\left(y-\dfrac12\right)^2+\dfrac{31}4

which has 3 extreme values over the interval -1\le y\le1 of 31/4 = 7.75 at the point (1, 1/2); 8 at (1, 1); and 10 at (1, -1).

  • If x=-1, then

f(-1,y)=8-y+y^2

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