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May 13th, 2019, 11:32 AM   #1
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What is 5x=25
Help me please.

3x=15
Solve for x please.
Thanks in advance.

x=15
Thanks.

In class, we started doing expressions like this: 3x=15
I don't really understand it.
Can someone give me a hand please? I don't have an idea where to start.
Thanks to anyone who will reply.

Last edited by skipjack; May 13th, 2019 at 07:18 PM.
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May 13th, 2019, 07:06 PM   #2
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5x = 25 implies (5x)/5 = 25/5, i.e. x = 5

3x = 15 implies x = 15/3 = 5

The equation x = 15 is already solved.

Note that 3x = 15 is called an equation, not an expression. It states that 3x and 15 are equal. It follows that a third of 3x is equal to a third of 15. A third of 15 is 5, so a third of 3x is 5. A third of 3x is x, so x is equal to 5, which is called the solution of the original equation.

Last edited by skipjack; May 13th, 2019 at 07:16 PM.
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May 13th, 2019, 08:01 PM   #3
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Math Focus: Algebraic Geometry
A tip that helped me when I first learned these is that your main goal is to get $x$ by itself on one side of the equal sign. You do this by doing the opposite of what's done to $x$ on both sides of the equal sign. For example, $3x=15$, since $3$ and $x$ are being multiplied, you just do the opposite of multiplication, division. So all you do is divide both sides by $3$ to get $x=\frac{15}{3}$, which is just $x=5$.
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Last edited by skipjack; May 13th, 2019 at 08:16 PM.
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