For all x > 0 and y > 0, the radical expression
sqrt _
Öx
----------
3Öx - Öy
Form the conjugate of the denominator. The conjugate of a
binomial is a binomial whose first term is the same as the
first term of the given binomial and whose second term is the
same as the second term of the given binomial, except that
its sign is changed. Therefore the conjugate of the
denominator 3Öx - Öy is the binomial 3Öx + Öy
Multiply the given expression by 1 written in the form of
(conjugate)/(conjugate) or (3Öx + Öy)/(3Öx + Öy)
_ _ _
Öx (3Öx + Öy)
---------- · ----------
3Öx - Öy (3Öx + Öy)
or
_ _ _
Öx(3Öx + Öy)
----------------------
(3Öx - Öy)(3Öx + Öy)
Use the distributive law on top, and FOIL on the bottom
__ __
3Öx² + Öxy
----------------------------
9Öx² + 3Öxy - 3Öxy - Öy²
The middle two terms cancel on the bottom
__ __
3Öx² + Öxy
----------------------------
9Öx² + 3Öxy - 3Öxy - Öy²
Take the square roots of the squares and get:
__
3x + Öxy
----------
9x - y
Edwin
AnlytcPhil@aol.com