Question

In solving the equation (x + 3)(x – 3) = -8, Eric stated that the solution would be
x + 3 = -8 => x = -11
or
(x – 3) = -8 => x = -5
However, 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

x^2 - 9 = 8

Answer 2

Is that what you're trying to do?

Answer 3

I don't understand it and I have to show step by step

Answer 4

Okay, are you trying to solve for x?

Answer 5

I believe it is trying to find out which one is incorrect at the soluitions and why it fails

Answer 6

okay

Answer 7

I don't see anywhere in the equation that talks about inequalities so I'll do solve it my way. Is that okay?

Answer 8

yes

Answer 9

The reason Eric was getting the wrong answer is because - 5 cannot be an answer. Even though - 11 is an answer, you cannot take two variables that are being multiplied and set them to equal zero without distributing first. You must first work out the equation so that x can be manipulated to get a constant value.

For instance,
(x-3)(x+3) =8

Subtract the 8 to the left side:
x^2 - 17 = 0
now add 17 to the right side to get x by itself.

Because x is squared, you must take the square root of both sides.

X will the be equal to : \[- and + \sqrt{17}\]

Answer 10

Does that make any sense?

Answer 11

yes thank u so much

Answer 12

No problem :D