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- [Voiceover] We have two
inequalities here, the first one
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says that x plus two is
less than or equal to two x.
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This one over here in I guess
this light-purple-mauve color,
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is three x plus four
is greater than five x.
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Over here we have four numbers
and what I want to do in this
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video is test whether
any of these four numbers
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satisfy either of these inequalities.
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I encourage you to pause this video and
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try these numbers out, does
zero satisfy this inequality?
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Does it satisfy this one?
Does one satisfy this one?
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Does it satisfy that one?
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I encourage you to try
these four numbers out
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on these two inequalities.
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Assuming you have tried that, let's work
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through this together.
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Let's say, if we try out
zero on this inequality
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right over here, let's substitute
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x with zero.
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So, we'll have zero plus two needs to
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be less than or equal to two times zero.
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Is that true?
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Well, on the left hand side,
this is two needs to be
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less than or equal to zero.
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Is that true, is two less
than or equal to zero?
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No, two is larger than zero.
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So this is not going to be
true, this does not satisfy
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the left hand side
inequality, let's see if it
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satisfies this inequality over here.
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In order to satisfy it,
three times zero plus four
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needs to be greater than five times zero.
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Well three times zero is just
zero, five times zero is zero.
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So four needs to be greater
than zero, which is true.
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So it does satisfy
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this inequality right over here so zero
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does satisfy this inequality.
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Let's try out one.
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To satisfy this one, one plus
two needs to be less than
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or equal to two.
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One plus two is three, is three
less than or equal than two?
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No, three is larger than two.
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This does not satisfy
the left hand inequality.
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What about the right hand
inequality right over here?
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Three times one plus four
needs to be greater than
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five times one.
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So three times one is three, plus four.
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So seven needs to be greater
than five, well that's true.
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Both zero and one satisfy
three x plus four is greater
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than five x, neither of them
satisfy x plus two is less than
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or equal to two x.
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Now let's go to the two.
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I know it's getting a
little bit unaligned,
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but I'll just do it all in the
same color so you can tell.
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Let's try out two here, two
plus two needs to be less than
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or equal to two times two.
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Four needs to be less
than or equal to four.
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Well four is equal to
four and it just has to be
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less than or equal, so this satisfies.
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This satisfies this inequality.
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What about this purple inequality?
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Let's see, three times
two plus four needs to be
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greater than five times two.
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Three times two is six plus four is ten,
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needs to be greater than 10.
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10 is equal to 10, it's
not greater than 10.
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It does not satisfy this inequality.
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If this was a greater than or equal to
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it would have satisfied but it's not.
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10 is not greater than 10.
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It would satisfy greater than or equal to
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because 10 is equal to 10.
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So two satisfies the left hand one but not
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the right hand one.
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Let's try out five.
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Five plus two needs to
be less than or equal
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to two times five, once
again everywhere we see
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an x, we replace it with a five.
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Seven needs to be less
than or equal to 10.
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Which is absolutely true,
seven is less than 10.
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So it satisfies less than or equal to.
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Five satisfies this
inequality and what you're
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probably noticing now is
that an inequality can
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have many numbers that satisfy.
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In fact they sometimes will
have nothing that satisfies it
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and sometimes they might
have an infinite number of
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numbers that satisfy it and
you see that right over here.
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We're just testing out a few numbers.
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For this left one, zero
and one didn't work,
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two and five did work.
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This right one, zero and
one worked, two didn't work.
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Let's see what five does.
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In order for five to
satisfy it, three times x.
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Now we're gonna try x being five.
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Three times five plus four
needs to be greater than
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five times five.
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Three times five is fifteen,
fifteen plus four is nineteen.
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Nineteen is to be greater
than 25, it is not.
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So five does not satisfy
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this inequality right over here.
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Anyway, hopefully you found that fun.