Divide by negative one and flip the sign
eg -x > 6
/ -1 /-1
x < - 6
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It changes the direction of the inequality.
When you multiply both sides by a negative number the inequality must be flipped over. You do not do that when multiplying by a positive number.
Yes, it is true.
For the same reason you must flip it when you multiply by a negative number. An example should suffice. 2 < 3 If you multiply by -1, without switching the sign, you get: -2 < -3, which is wrong. Actually, -2 > -3. Look at a number line if you are not sure about this - numbers to the left are less than numbers further to the right. Dividing by a negative number is the same as multiplying by the reciprocal, which in this case is also negative. These signs are strictly the "Greater than" and "Less than" signs. The inequality sign is an = with a / stroke through it. If you divide an inequality by -1 it remains an inequality.
Dividing or multiplying by a negative reverts the value to the other side of the number line, thus, the inequality sign must revert as well.