Write [tex]$x^2 + y^2 - 18x + 8y + 5 = 0$[/tex] in standard form.

1. Group terms and move the constant to the other side of the equation.
[tex]\[ x^2 - 18x + y^2 + 8y = -5 \][/tex]

2. Determine the values that need to be added to both sides of the equation.
[tex]\[ \left(-\frac{18}{2}\right)^2 = 81 \quad \text{and} \quad \left(\frac{8}{2}\right)^2 = 16 \][/tex]

3. Add the values to both sides of the equation.
[tex]\[ x^2 - 18x + 81 + y^2 + 8y + 16 = -5 + 81 + 16 \][/tex]

4. Write each trinomial as a binomial squared, and simplify the right side.
[tex]\[ (x - 9)^2 + (y + 4)^2 = 92 \][/tex]

What is the standard form of the equation of a circle given by [tex]$x^2 + y^2 - 18x + 8y + 5 = 0$[/tex]?

[tex]\[ (x - 9)^2 + (y + 4)^2 = 92 \][/tex]



Answer :

To rewrite the equation [tex]\( x^2 + y^2 - 18x + 8y + 5 = 0 \)[/tex] in standard form, we need to complete the square for the [tex]\( x \)[/tex]-terms and the [tex]\( y \)[/tex]-terms. Let's go through the process step-by-step.

1. Group terms and move the constant to the other side of the equation:
[tex]\[ x^2 - 18x + y^2 + 8y = -5 \][/tex]

2. Determine the values that need to be added to both sides of the equation:

- For [tex]\( x \)[/tex]-terms:
[tex]\[ (-18 \div 2)^2 = (-9)^2 = 81 \][/tex]

- For [tex]\( y \)[/tex]-terms:
[tex]\[ (8 \div 2)^2 = 4^2 = 16 \][/tex]

3. Add the values to both sides of the equation:
[tex]\[ x^2 - 18x + 81 + y^2 + 8y + 16 = -5 + 81 + 16 \][/tex]

Simplifying the right side:
[tex]\[ x^2 - 18x + 81 + y^2 + 8y + 16 = 92 \][/tex]

4. Write each trinomial as a binomial squared, and simplify the right side:
[tex]\[ (x - 9)^2 + (y + 4)^2 = 92 \][/tex]

Therefore, the standard form of the given equation [tex]\( x^2 + y^2 - 18x + 8y + 5 = 0 \)[/tex] is:
[tex]\[ (x - 9)^2 + (y + 4)^2 = 92 \][/tex]