# a+b=m , a-b=?

#### idontknow

If $$\displaystyle a+b=m$$ , express $$\displaystyle a-b$$ in terms of m .
$$\displaystyle a-b=f(m)=$$?

greg1313

#### phillip1882

so lets take some examples and see if we can figure out a rule.
2+3 = 5
2-3 = -1
4+2 = 6
4 -2 = 2
7 +11 = 18
7 - 11 = -4
so it looks like our rule is:
if a +b = m
a -b = m -2b

#### mathman

Forum Staff
If $$\displaystyle a+b=m$$ , express $$\displaystyle a-b$$ in terms of m .
$$\displaystyle a-b=f(m)=?$$
Doubtful. Example: m=0, then a+b=0. As a result let a=x thus b=-x so a-b=2x, where x can be any number. So f(m)=2x, not at all defined.

idontknow

#### topsquark

Math Team
If $$\displaystyle a+b=m$$ , express $$\displaystyle a-b$$ in terms of m .
$$\displaystyle a-b=f(m)=$$?
Or, in symbols:
a + b = m
a - b = a + (b - 2b) = (a + b) - 2b = m - 2b

-Dan

idontknow