WEBVTT

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Solve for a and
check your solution.

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And we have a plus
5 is equal to 54.

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Now, all this is
saying is that we

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have some numbers,
some variable a.

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And if I add 5 to
it, I will get 54.

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And you might be able
to do this in your head.

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But we're going to do it a
little bit more systematically.

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Because that'll be
helpful for you when we

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do more complicated problems.

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So in general, whenever you
have an equation like this,

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we want to have the variable.

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We want this a all by itself
on one side of the equation.

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We want to isolate it.

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It's already on
the left-hand side,

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so let's try to get
rid of everything

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else on the left-hand side.

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Well, the only other thing
on the left-hand side

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is this positive 5.

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Well, the best way to get rid
of a plus 5, or a positive 5,

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is to subtract 5.

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So let's subtract 5.

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But remember, this says
a plus 5 is equal to 54.

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If we want the
equality to still hold,

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anything we do to the left-hand
side of this equation,

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we have to do to the right
side of the equation.

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So we also have to
subtract 54 from the right.

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So we have a plus 5 minus 5.

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Well, that's just
going to be a plus 0.

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Because if you add 5 and you
subtract 5, they cancel out.

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So a plus 0 is just a.

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And then 54 minus 5, that is 49.

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And we're done.

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We have solved for a.

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A is equal to 49.

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And now we can check it.

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And we can check it by
just substituting 49 back

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for a in our original equation.

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So instead of writing a
plus 5 is equal to 54,

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let's see if 49 plus
5 is equal to 54.

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So we're just
substituting it back in.

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49, 49 plus-- let me do that
in that same shade of green.

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49 plus 5 is equal to 54.

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We're trying to check this.

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49 plus 5 is 54.

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And that, indeed,
is equal to 54.

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So it all checks out.