Thread: very confusing!

Could you please tell me why the + sign is changed to a - (minus) in this problem:

(-5) (x+4y+5)

= -5x + (-5) (4y) + (-5) (5)
= -5x - 20y - 25
they changed the + to - and 20y and 25 became positive instead of negative.

Does the first number outside of the parenthesis have something to do with this? It only happens when the first number is negative. Its a little confusing because thats not how we were taught to multiply signed numbers.

I really hope I get through this algebra stuff!!
Thanks again,
Rainie

Originally Posted by RainieB

Could you please tell me why the + sign is changed to a - (minus) in this problem:

(-5) (x+4y+5)

= -5x + (-5) (4y) + (-5) (5)
= -5x - 20y - 25
they changed the + to - and 20y and 25 became positive instead of negative.

Does the first number outside of the parenthesis have something to do with this? It only happens when the first number is negative. Its a little confusing because thats not how we were taught to multiply signed numbers.

I really hope I get through this algebra stuff!!
Thanks again,
Rainie

ur question is a bit confusing.
can u clarify which + changed to -?

Originally Posted by RainieB

Could you please tell me why the + sign is changed to a - (minus) in this problem:

(-5) (x+4y+5)

= -5x + (-5) (4y) + (-5) (5)
= -5x - 20y - 25
they changed the + to - and 20y and 25 became positive instead of negative.

Did you mean "negative instead of positive"? -20y and -25 are negative.

Does the first number outside of the parenthesis have something to do with this? It only happens when the first number is negative. Its a little confusing because thats not how we were taught to multiply signed numbers.

Then how were you taught to multiply signed numbers? I was certainly taught that "negative times positive is negative" so (-5)(4)= -20 and (-5)(5)= -25, exactly what you have.

I really hope I get through this algebra stuff!!
Thanks again,
Rainie[/QUOTE]

This is what I thought it should be :

(-5) (x+4y+5)

= -5x + (-5) (4y) + (-5) (5)
= -5x + -20y + -25

The minus signs I had originally were subtraction. Yes multiply a negative x positive is negative, but this is what they had in the text:

=-5 - 20y - 25

I think they are showing 20y and 25 as positive!

Originally Posted by RainieB

I think they are showing 20y and 25 as positive!

It sounds as though you are not familiar with negative numbers, since you feel that "+(-20y)" is "positive". To clarify the topic, please try this lesson on negative numbers, which explains, in part, how adding a negative and subtracting a positive are the same thing.