Put x=b+z; then, from the first equation, y=b-z.

S. A.

11

151. Equations with more than two unknown quantities. No general rules can be given for the solution of simultaneous equations of the second degree with more than two unknown quantities: all that can be done is to solve some typical examples.

Also from the original equations it is clear that the signs must all be positive or all be negative.

Add (v) and (vi) and subtract (iv) from the sum; then

I. If x=y, we have from (ii) and (iii) by subtraction