May 13th, 2019, 11:32 AM  #1 
Newbie Joined: May 2019 From: London Posts: 18 Thanks: 0 
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. 
May 13th, 2019, 07:06 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,921 Thanks: 2203 
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. 
May 13th, 2019, 08:01 PM  #3 
Member Joined: Oct 2018 From: USA Posts: 88 Thanks: 61 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 $x=5$.
Last edited by skipjack; May 13th, 2019 at 08:16 PM. 

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algebra, arithmetic, equations, expression, solve, solve for x 
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