Math Problem Statement

If real numbers x,y>0x,y>0 and 18x2+2y=1x218​+y2​=1, find the minimum value of x+yx+y.

Solution

We are given the system of equations for xx and yy:

18x2+2y=1andx+y=118x^2 + 2y = 1 \quad \text{and} \quad x + y = 1

We need to find the minimum value of x+yx + y. Let’s start by solving the system step by step.

Step 1: Solve for yy from the second equation

The second equation is:

x+y=1x + y = 1

Solving for yy, we get:

y=1xy = 1 - x

Step 2: Substitute y=1xy = 1 - x into the first equation

Now, substitute y=1xy = 1 - x into the first equation:

18x2+2(1x)=118x^2 + 2(1 - x) = 1

Simplifying this:

18x2+22x=118x^2 + 2 - 2x = 1

18x22x+2=118x^2 - 2x + 2 = 1

18x22x+1=018x^2 - 2x + 1 = 0

Step 3: Solve the quadratic equation

We need to solve the quadratic equation:

18x22x+1=018x^2 - 2x + 1 = 0

We can use the quadratic formula to find the values of xx:

x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

For the equation 18x22x+1=018x^2 - 2x + 1 = 0, we have a=18a = 18, b=2b = -2, and c=1c = 1. Plugging these values into the quadratic formula:

x=(2)±(2)24(18)(1)2(18)x = \frac{-(-2) \pm \sqrt{(-2)^2 - 4(18)(1)}}{2(18)} x=2±47236x = \frac{2 \pm \sqrt{4 - 72}}{36} x=2±6836x = \frac{2 \pm \sqrt{-68}}{36}

Since the discriminant is negative (68\sqrt{-68}), there are no real solutions for xx. Therefore, this system does not have a real solution for xx and yy. Hence, the minimum value of x+yx + y is not attainable in real numbers.

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Math Problem Analysis

Mathematical Concepts

Algebra
Quadratic Equations
Optimization

Formulas

Quadratic equation formula ax^2 + bx + c = 0
Substitution method

Theorems

Quadratic formula
Minimum value of a function

Suitable Grade Level

Grades 9-11