A plus b equals 8 and a minus b equals 9?
Solve one of the formulas for A, then substitute that into the
other formula to solve for B, then substitute the solution for B
into one of the formulas to solve for A.
Here is how:
Givens:
A+B=8
A-B=9
So:
If A+B=8 then A=8-B
Next, substitute this into the other formula...
A-B=9
(8-B)-B=9
(-B) - B = 1
(-2B) = 1
B= (- 1/2)
Next, substitute the solution for B into one of the formulas to
solve for A....
A+B=8
A+ (-1/2) = 8
A = 8 and 1/2
So...
B= (- 1/2)
A = 8 and 1/2