Solving Algebraic Expressions: Addition and Subtraction

Let’s solve a very simple algebraic expression that involves addition and subtraction. Here’s the first example.

4 + x = 12

The above is a very simple algebraic expression that can also be classified as a “simultaneous equation.” That’s because both sides of the equal side will produce the same result. In other words, both sides of the equal sign are “simultaneous.”

Here are your instructions:

In the algebraic expression above, find the value of “x” by first simplifying and then solving the equation.

Remember, simplifying an algebraic expression and solving it are two different things. Simplifying an algebraic expression brings you closer to finding out the value of the unknown number. Solving it gives you the unknown value.

So, we will simplify the algebraic expression by grouping like terms together. Let’s look at our equation again:

4 + x = 12.

Let’s leave the “x” on one side of the equation and move the 4 to the other side with the 12.

So it becomes: x = 12 – 4.

So why does it become 12 – 4 and not 12 + 4?

Remember the rule: when we transition numbers or symbols from one side of an equation to the other, the value of that number or symbol changes from negative to positive or positive to negative.

On the left side of the equal sign, the 4 had a positive value. When we “transition” it to the right side, it changes to a negative value.

Up Next: Solving Multiplication Problems in Algebra by Dividing.

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