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5.8 number 18.
Here we want to subtract 8x squared plus 7x minus 8 from
5x squared plus 2x minus 7.
Now, the most common mistake here is to subtract these in
the wrong order.
So for a second, let's just think
about a different question.
What would we get if we subtracted 3 from 7?
Well, that would give us 4, because we do 7 take away 3.
Now, notice that the second number that was mentioned is
the one that goes on top.
We're subtracting the first number from it.
Same thing applies here.
The second one that was mentioned, the 5x squared plus
2x minus 7 goes on top.
We're subtracting the other one from it.
So now the way we want to set it up is 5x squared plus 2x
minus 7 take away the entire quantity of 8x squared
plus 7x minus 8.
So It's very important to put parentheses here to remind
yourself that everything, every piece of term here, is
being subtracted.
That means that this minus sign is going to distribute on
to every term.
So now we can go ahead and do the subtractions.
5x squared take away 8x squared is minus 3x squared.
2x take away 7 is minus 5x.
Minus 7 minus a minus 8.
If we look at that off to the side, minus 7
minus a negative 8.
Add the opposite.
Minus 7 plus 8 gives us plus 1.
And that's our final answer.