Solve the Expression: Evaluating 5x-6 When x=8

Variable Substitution with Integer Values

What will be the result of this algebraic expression:

5x6 5x-6

if we place

x=8 x=8

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:07 First, substitute and solve.
00:10 Let's put in the right values from the data we have, and solve the problem step by step.
00:16 Remember, always do multiplication and division before adding and subtracting.
00:22 Now, let's keep solving using the correct order of operations.
00:26 And that's how we find the solution to the problem.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

What will be the result of this algebraic expression:

5x6 5x-6

if we place

x=8 x=8

2

Step-by-step solution

To answer the question we first need to understand what X is.

X is an unknown, meaning it's a symbol that represents another number, an unknown one, that could be there in its place.

Usually in exercises we'll need to calculate and discover what X is appropriate for each exercise,

but in this case the result is given to us: X=8
Therefore, we can substitute (plug in) the value 8 everywhere X appears in the exercise.

So we get:

5*8-6

40-6
34

3

Final Answer

34

Key Points to Remember

Essential concepts to master this topic
  • Substitution Rule: Replace the variable with its given value everywhere
  • Technique: Calculate 5×86=406=34 5 \times 8 - 6 = 40 - 6 = 34 step by step
  • Check: Substitute back: when x=8, 5(8)6=34 5(8)-6 = 34

Common Mistakes

Avoid these frequent errors
  • Forgetting to follow order of operations
    Don't calculate 5×8-6 as 5×(8-6) = 5×2 = 10! This ignores order of operations and gives the wrong answer. Always multiply first: 5×8 = 40, then subtract: 40-6 = 34.

Practice Quiz

Test your knowledge with interactive questions

What will be the result of this algebraic expression:

\( 5x-6 \)

if we place

\( x=8 \)

FAQ

Everything you need to know about this question

What does it mean to substitute x=8?

+

Substitution means replacing the variable with its given value. Wherever you see x in the expression, put 8 in its place. So 5x6 5x-6 becomes 5(8)6 5(8)-6 .

Why do I multiply 5×8 before subtracting 6?

+

This follows the order of operations (PEMDAS)! Multiplication comes before subtraction, so you must calculate 5×8=40 5 \times 8 = 40 first, then subtract: 406=34 40 - 6 = 34 .

Do I need parentheses when substituting?

+

It's good practice to use parentheses: 5(8)6 5(8)-6 instead of 586 58-6 . This prevents confusion and makes it clear you're multiplying 5 by 8.

How can I check if my answer is correct?

+

Substitute your answer back! If 5x6=34 5x-6 = 34 when x=8, then 5(8)6 5(8)-6 should equal 34. Calculate: 406=34 40-6 = 34

What if x had a different value?

+

The process stays the same! If x=3, then 5x6=5(3)6=156=9 5x-6 = 5(3)-6 = 15-6 = 9 . Always substitute first, then calculate using order of operations.

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