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someone explain in simple english how to solve inequalities using multiplicatino and division please

 Apr 6, 2015

Best Answer 

 #1
avatar+128578 
+5

This is often confusing.....You just have to remember to "reverse" the inequality sign if you multiply or divide by a negative..

Example

3x >  6      divide both sides by 3

x  > 2   and this is true because if x = 4.....then  3(4) > 6  →  12 > 6

But, notice.....what if we had.....

-3x  > 6     divide both sides by -3 and reverse the sign

x <  -2       the reason for this is that if we kept the sign  as  ">"    we'd have an error

Note the error, here......

-3x >  6     divide by -3 and don't reverse the sign

x > -2        but if x > -2, then 0 should work in the original problem, right???

But  -3(0) > 6   =   0 > 6    and this clearly isn't true

 

So....by reversing the sign  we have x < -2   so..... something like -4 should work in the original problem

So.....

-3(-4) > 6    implies that 12 > 6 and that's true......!!!

 

So....just remember.....multiplying or dividing by a negative means that we have to reverse the signs  !!!

 

  

 Apr 6, 2015
 #1
avatar+128578 
+5
Best Answer

This is often confusing.....You just have to remember to "reverse" the inequality sign if you multiply or divide by a negative..

Example

3x >  6      divide both sides by 3

x  > 2   and this is true because if x = 4.....then  3(4) > 6  →  12 > 6

But, notice.....what if we had.....

-3x  > 6     divide both sides by -3 and reverse the sign

x <  -2       the reason for this is that if we kept the sign  as  ">"    we'd have an error

Note the error, here......

-3x >  6     divide by -3 and don't reverse the sign

x > -2        but if x > -2, then 0 should work in the original problem, right???

But  -3(0) > 6   =   0 > 6    and this clearly isn't true

 

So....by reversing the sign  we have x < -2   so..... something like -4 should work in the original problem

So.....

-3(-4) > 6    implies that 12 > 6 and that's true......!!!

 

So....just remember.....multiplying or dividing by a negative means that we have to reverse the signs  !!!

 

  

CPhill Apr 6, 2015

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