First you have to subtract from both sides. These problems are set up and ready to solve. This is the solution Khan Academy gave.
And once again we have three equations with three unknowns.
Find The Equation Of A Circle With Center 1 4 And Radius 3. Solve system with substitution. If ab is the solution to the system then what is the value of b - a. This problem presents two equations one of which is already ready for substitution.