The given equation is:
[tex]x^2+6x=1[/tex]
To complete the square, find the coefficient of x,
The coefficient of x is +6x,
Half the coefficient of x is:
[tex]\frac{1}{2}\times(+6)=+3[/tex]
Therefore, to make it a perfect square calculate add the square of 3 to both sides of the equation.
The square of 3 is:
[tex]3^2=9[/tex]
Therefore, the term that must be added is 9.
Therefore, the correct answer is choice C:
9
