1 - 1 = 1
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4x-12 2x-6 x^2-3x
Solve the equation (its subtracting the first two fractions and equalling the last fraction)
browsers override your text formatting. I think you meant
1/(4x-12) - 1/(2x-6) = 1/(x^2-3x)
Factoring the denominators, you have
1/4(x-3) - 1/2(x-3) = 1/x(x-3)
Clearly the LCD is 4x(x-3). So, using that LCD, you have in the top
1(x) - 1(2)(x) = 1(4)
x-2x=4
x = -4
You can disregard the denominators here, because they are all the same.
If just evaluating an expression, you have to keep the denominators, but not if solving an equation.
As long as no denominator is zero!