The general form of the equation of a circle is,
x² + y² + Dx + Ey + F = 0, where D, E, F are constants.
The given equation is 7x² + 7y² − 28x + 42y − 35 = 0. So, to convert this equation into a general form we just need to get rid of the leading coefficient 7.
Hence, divide both sides of the equation by 7. So,
x² + y² − 4x + 6y − 5=0.
So, the general form of the equation is x² + y² − 4x + 6y − 5=0.