Q. A circle in the xy-plane has the equation 4x2+4y2−24x=28. What is the diameter of the circle?
Write Circle Equation: Write the given equation of the circle.The given equation is 4x2+4y2−24x=28.We need to complete the square for both x and y to bring the equation into standard form.
Factor Out Coefficients: Factor out the coefficient of x2 and y2.Since the coefficients of x2 and y2 are both 4, we factor them out to make completing the square easier.4(x2+y2−6x)=28
Complete Square for x: Complete the square for the x-term.To complete the square, we take the coefficient of x, divide it by 2, and square it. Then we add and subtract this value inside the parenthesis.4(x2−6x+9−9+y2)=28
Add Value to Equation: Add the value we subtracted to the other side of the equation.We added and subtracted 9 inside the parenthesis, but since it's multiplied by 4, we need to add 4×9 to the other side of the equation.4(x2−6x+9+y2)=28+4×94(x2−6x+9+y2)=28+364(x2−6x+9+y2)=64
Write Completed Square: Write the completed square for the x-term and simplify the equation.(x−3)2 is the completed square for the x-term, and we simplify the right side of the equation.4((x−3)2+y2)=64
Divide by Coefficient: Divide both sides by the coefficient of the completed squares to get the standard form of the circle's equation.(x−3)2+y2=464(x−3)2+y2=16
Identify Circle Radius: Identify the radius of the circle from the standard form equation.The standard form of a circle's equation is (x−h)2+(y−k)2=r2, where (h,k) is the center and r is the radius. From our equation, r2=16, so r=4.
Calculate Circle Diameter: Calculate the diameter of the circle.The diameter D of a circle is twice the radius r, so D=2r.D=2×4D=8
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