The way we can find the error in the proof is if we go through it line by line. It might sound tedious, but thankfully, there are only three lines. The first one is the given equation. Nothing wrong with that. The second is subtracting three from both sides. That seems right too since 3 – 3 = 0 and 28 – 3 = 25. No problems there. That must mean the error is in the third line. But the square root of 25 is 5, so where's the problem. Well, *z* = 5 is only one of the answers. Couldn't *z* = -5 be an answer too? Yes, it could. That's what the proof didn't consider. |