Q. Write the equation in standard form for the circle x2+y2+6x−1=0.
Identify equation and need: Identify the given equation and the need to complete the square for the x-terms.The given equation is x2+y2+6x−1=0. To write the equation in standard form, we need to complete the square for the x-terms.
Group x-terms and leave space: Group the x-terms together and leave a space to complete the square.x2+6x+()+y2=1We have moved the constant term to the other side by adding 1 to both sides.
Find number to complete square: Find the number to complete the square for the x-terms.To complete the square, we take half of the coefficient of x, which is 26=3, and square it, giving us 32=9.
Add and subtract inside parentheses: Add and subtract the number found in Step 3 inside the parentheses.x2+6x+9−9+y2=1We added 9 to complete the square and then subtracted 9 to keep the equation balanced.
Rewrite equation with completed square: Rewrite the equation with the completed square for the x-terms.(x+3)2−9+y2=1We have now completed the square for the x-terms.
Move constant term from completed square: Move the constant term from the completed square to the other side.(x+3)2+y2=1+9We added 9 to both sides to isolate the completed square and y2 on one side.
Simplify right side of equation: Simplify the right side of the equation.(x+3)2+y2=10We have combined the constants on the right side.
Write final equation in standard form: Write the final equation in standard form.The standard form for the equation of a circle is (x−h)2+(y−k)2=r2, where (h,k) is the center and r is the radius. Our equation is now in this form with h=−3, k=0, and r2=10.
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