Question

please help me....how do you solve the equation (x + 4)(x – 7) = -18, Eric stated that the solution would be x+4=-18=>x=-22 or (x-7)=-18=>x-11However, at least one of these solutions fails to work when substituted back into the original equation. Why is that? Please help Eric to understand better; solve the problem yourself, and explain your reasoning

Answer 1

You have two answers for x, one of them is -2 and the other is.....5

Answer 2

Eric should have simplified and set the equation equal to zero first.

Answer 3

i dont understand them with the => sign in it

Answer 4

I think the '=>' are just supposed to be arrows.

Answer 5

ok, What doesn't make sense?

Answer 6

not sure what the sign means

Answer 7

Did you try checking those solutions {-2, 5} in the original equation?

Answer 8

not yet i will try now. It will take me a few i have a fractured right hand and it is casted and cant right well. much easier to type the write.

Answer 9

"x+4=-18=>x=-22 or (x-7)=-18=>x-11"
means
\[\large x+4=-18 \rightarrow x=-22\]
\[\large x-7=-18 \rightarrow x=-11\]

Answer 10

oic ty for explaining

Answer 11

You should be able to check those solutions mentally.

Answer 12

I am still learning I have to write it down to be sure I am doing it right

Answer 13

oh k

Answer 14

when I check them they both are correct

Answer 15

Bah, my mistake, they do work. Sorry. I missed one of the negative signs when I worked it out the first time.
Regardless, you still need to figure out why those are the solutions.

Answer 16

@zordoloom , sorry, my error, but still: could you explain how you got those answers instead of breaking the code of conduct by just giving answers?

Answer 17

Do this, distribute, and then use the quadratic formula.

Answer 18

(Can also factor, if you don't want to use the QF)

Answer 19

true.

Answer 20

Just ditribute:---> x^2-3x-10=0, then factor and you get (x+2)(x-5)=0

Answer 21

This makes it easier than using the quad. form.

Answer 22

k ty

Answer 23

so is that wh

Answer 24

Do you know how to factor?

Answer 25

somewhat not real well

Answer 26

That's fine. Here, distribute first. (x+4)(x-7)=18
you get (x*x+x*-7+4*x+4*-7)=-18

Answer 27

When you simplify like therms you get (x^2-3x-28)=-18

Answer 28

now move the -18 to the left side to make the equation equal to 0

Answer 29

you now have x^2-3x-10=0

Answer 30

This now factors into (x+2)(x-5)=0

Answer 31

Now you have (x+2)=0 and (x-5)=0, all what you have to do is solve for x for each equatoin.

Answer 32

x-5=0, move the x to the right side, x=5, do the same with the other equation, x+2=0 move the 2 to the other side, x=-2.

Answer 33

You are doing simple algebra here.

Answer 34

ok i see how you are doing that

Answer 35

You can't just solve x+4=-18 like you did in your question. The equation must have been set to 0 first.

Answer 36

ok so which equation is the right one

Answer 37

I'm not sure what your question is. Since this is a second degree polynomial (an equation that has x squared when you distribute) it must have two answers. Those two answer were x=5, and x=-2