That's the whole point in multiplying by -1, that we'll get positive numbers instead of negative numbers, and the equation is still valid because we'll be doing it to both sides.
Now, I don't like having negative numbers in my equations, and since both sides are negative, I'll multiply both sides by -1 to convert these to positive numbers. Subtracting a positive number from a negative numbers makes that number more negative. Then the -2 on the right side becomes a -5. We have the "+ 3" on the left side that can be eliminated there. The next thing we can do is subtract 3 from both sides. The 5x - 5x part cancels out, leaving just a -2 for the right hand side. For the right hand side, you have 5x - 5x - 2. On the left side, you have 2x - 5x, which is -3x, and then you have that + 3, so you have -3x + 3 for the left hand side. He actually subtracts 2x, but when you subtract 5x from both sides, you have: At that point in the video, his equation is 2x + 3 = 5x - 2.
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