Answer:
![P=4x+9](https://tex.z-dn.net/?f=P%3D4x%2B9)
Step-by-step explanation:
Basically, the problem is asking to make an triangle but without labeling its sides as number, but as algebraic expression.
So, let's say that all three sides are
![AB=x+1\\BC=x+3\\AC=2x+5\\](https://tex.z-dn.net/?f=AB%3Dx%2B1%5C%5CBC%3Dx%2B3%5C%5CAC%3D2x%2B5%5C%5C)
Now, remember that the perimeter is the sum of all sides of a figure, so in this case would be
![P=(x+1)+(x+3)+(2x+5)](https://tex.z-dn.net/?f=P%3D%28x%2B1%29%2B%28x%2B3%29%2B%282x%2B5%29)
To simplify this expression, we just need to reduce like terms as follows
![P=(x+1)+(x+3)+(2x+5)\\P=(x+x+2x)+(1+3+5)\\P=4x+9](https://tex.z-dn.net/?f=P%3D%28x%2B1%29%2B%28x%2B3%29%2B%282x%2B5%29%5C%5CP%3D%28x%2Bx%2B2x%29%2B%281%2B3%2B5%29%5C%5CP%3D4x%2B9)
Therefore, the simplified expression of the perimeter is
![P=4x+9](https://tex.z-dn.net/?f=P%3D4x%2B9)
The image attached shows the triangle we used.