What would the LCD be between x^2, 4x, and 6? Here is the problem: 1/x^2+3/4x-5/6

Do it just like you would with numbers

x^2 = x*x
4x = 2*2*x
6 = 2*3

we will need x*x

look at the second set of factors
we will need 2*2*x , but we already have an x
so far we need
2*2*x*x

look at the last group
we will need a 2*3
but we already have the 2, so just include a 3

LCD = 2*2*3*x*x = 12x^2

notice that 12x^2 divides evenly by each of the other denominators