(х^2-y^2)/(6a-3b) : (y-x)/(4a^2-b^2) = ((x-y)(x+y))/(3(2a-b)) : (y-x)/((2a-b)(2a+b)) = ((x-y)(x+y))/(3(2a-b)) × ((2a-b)(2a+b))/(-(x-y)) = ((x+y)(2a+b))/(-3)
(х^2-y^2)/(6a-3b) : (y-x)/(4a^2-b^2) = ((x-y)(x+y))/(3(2a-b)) : (y-x)/((2a-b)(2a+b)) = ((x-y)(x+y))/(3(2a-b)) × ((2a-b)(2a+b))/(-(x-y)) = ((x+y)(2a+b))/(-3)