Another multiplying binominals

[Guest]

(x-1)(x+2)-(x+3)(x-4)

I tried to use the foil method on each but I ended up with the following.
2x^2+2x-x-2
2x^2+x-2 and

-x^2+4x+3x-12
-x^2+7x-12

I was going to combine like terms but I looked in the back of our book for the answer to make sure I was on the right track and found the answer to be 2x+10. There is no way to reach that with these figures. So I am confused.

Where did I go wrong?

 

[happy]

(x-1)(x+2)-(x+3)(x-4)

I tried to use the foil method on each but I ended up with the following.
2x^2+2x-x-2
2x^2+x-2 and

-x^2+4x+3x-12
-x^2+7x-12

Wrong x*x= 2x^2?????? No, x*x = x^2

It should be...

x^2 +x -2 - (x^2-x-12)

Now tell me what you get?

 

[Guest]

Okay, I am with you so far.

I get like mental blocks when I am doing Math or something.

I am at x^2+x-2 and I have to subtract x^2-x-12 from that. I am thinking that the x^2 will cancel each other out as will the x's but that leaves me to the problem of knowing the answer is 2x+10. That was probably my mistake looking at the answer because now I am convinced that I did the problem wrong and I don't know how to proceed.

 

[Denis]

Okay, I am with you so far.
I get like mental blocks when I am doing Math or something.
I am at x^2+x-2 and I have to subtract x^2-x-12 from that. I am thinking that the x^2 will cancel each other out as will the x's but that leaves me to the problem of knowing the answer is 2x+10. That was probably my mistake looking at the answer because now I am convinced that I did the problem wrong and I don't know how to proceed.

Ohhhhhhhhhhhhhhhhhh bethany.....

"I am at x^2+x-2 and I have to subtract x^2-x-12 from that"

x^2 - x^2 = 0 : so they cancel out, as you say; good!
x - (-x) = x + x = 2x : they DO NOT cancel out; capish?
-2 - (-12) = -2 + 12 = 10

So we're left with 2x + 10 ; see that medeer?

REMEMBER that a - (-b) = a + b ; two minuses make a plus

 

[Guest]

OOOOOOOOOOOOh. :idea: Why didn't I see that? You are to good to me. Thank you so much.
I don't understand why when I'm doing a problem I go blank. I start working it out then I freeze. I don't know if it is because I don't have the confidence to go forward or I am afraid of getting it wrong or what. I know this site doesn't offer that kind of counseling, so I will sign off for now. :wink: Thanks again.