GCF(18xy, 15xy) = 3xy LCM(18xy, 15xy) = 90xy
30xy
It is not possible to give a sensible answer to this question. The least common multiple (LCM) refers to a multiple that is COMMON to two or more numbers (or expressions). You have only one expression in the question: 15xy. Also, if 5x3y is different from 15xy then multiplication is not commutative in whatever set these belong to. In that case it is impossible to find the LCM without information about the rules of "multiplication" in this set.
LCM(12x, 8y) = 24xy.
The LCM is 1320.
√(12x3y3z-2) * √(15xy) = √(180x4y4x-2) = 13.416x2y2z-1 = 13.416(xy)2/z
120x
LCM(5x, 12x) = 60x
12x
LCM(12x, 40y3) = 120xy3
Since 36ab is a multiple of 4b, it is automatically the LCM of this problem.
That will depend on the value of x