如何計........................

x^n indicates x的n次方

3-2x^2-3x-7x+5x^2-7
First we have to simplify it:
3-7-2x^2+5x^2-3x-7x (Collecting like terms)
-4+3x^2-10x
Then we have to arrange it in descending powers of x.
Which means greater the index is, it will be arranged first.
-4+3x^2-10x
=3x^2-10x-4

5-2x^2-5x-9x-3x^2+7
=5+7-2x^2-3x^2-5x-9x
=12-5x^2-14x
This time we have to arrange it in ascending power of x.
It is the opposite of descending power.
12-14x-5x^2