Answer:

Step-by-step explanation:
The sum you are trying to understand is this.

Remember that in general when you have a geometric series
you have that
and that equality is true as long as
.
Therefore here we have
and 
Therefore we can use the formula and

The smallest exponents of the x and y term are 2. The Greatest Common Factor ( G C F ) for 9 x² y² and 5 x² y³ is: x² y².
6x/-4 = 6(-1/2)
6x/-4 = - 3...multiply by -4
6x = -3 * -4
6x = 12
x = 2