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# Given that 2x-5=3(2x-2)-15, WHAT IS THE EVALUATION OF 2X+1?

what is the evaluation?

### 3 Answers by Expert Tutors

Robert J. | Certified High School AP Calculus and Physics TeacherCertified High School AP Calculus and Ph...
4.6 4.6 (13 lesson ratings) (13)
1
Let u = 2x+1. Then 2x-5 = 2x+1-6 = u-6, and 2x-2 = 2x+1-3 = u-3.
So,
2x-5=3(2x-2)-15 becomes,
u-6 = 3(u-3)-15=> u-6 = 3u-24
=> 18 = 2u
=> u = 9
Arthur D. | Effective Mathematics TutorEffective Mathematics Tutor
5.0 5.0 (7 lesson ratings) (7)
0
2x-5=3(2x-2)-15
2x-5=6x-6-15
2x-5=6x-21
21-5=6x-2x
16=4x
x=4
2x+1=2(4)+1=8+1=9
Simon S. | Purveyor of Analytical ToysPurveyor of Analytical Toys
4.9 4.9 (127 lesson ratings) (127)
0
One thing which might be confusing in this problem is the wording. "What is the evaluation of 2x+1" is just funky math-speak for "what number is 2x+1 once you plug in x." To do this, we can solve the equation they give us, and then we'll plug in x.

Let me show you a similar example: Given that  3x - 2 = 4(2x - 2) - 14, what is the evaluation of 3x + 2?

We'll start by solving for x:
3x - 2  =  4(2x - 2) - 14
3x - 2  =   8x - 8    - 14
3x - 2  =  8x - 22
+22        +22

3x + 20  =  8x
-3x             -3x

20  =  5x
/5       /5

4    =  x

Now we know that x is 4. Therefore, 3x+2 evaluates to  3(4) + 2,  which is better known to its friends as 14.

Take home message: The phrase "evaluation" means "what number do you get when you plug in for all of the variables." Hopefully this is enough to help you make some progress. :-)