To find x, first we'll split the triangle in two right triangles.
The first triangle will be the one with sides (8,x+4,y) and the second triangle will be the one with sides (12,2x+1,y).
As you can see, these two triangles share the side 'y'.
To solve we'll do the following; first solve for 'y' by applying the Pythagorean theorem in the second triangle, and finally solve for 'x' applying Pythagorean theorem in the first triangle.
From the second triangle (12,2x+1,y) we solve for 'y' by writing:
![y^(2)=12^(2)- (2x+1)^(2)=144-4 x^(2) -4x-1=](https://img.qammunity.org/2019/formulas/mathematics/high-school/lqro4ay1tm9k6vjpzf967rv8e3pks4g4wo.png)
Now that we know 'y^2' we apply Pythagorean Theorem in the first triangle (8,x+4,y)
![8^(2)= (x+4)^(2)+ y^(2)= (x^(2)+8x+16)+(143-4 x^(2) -4x)](https://img.qammunity.org/2019/formulas/mathematics/high-school/iprualga7eqh9f6heu9wk9znv8hpg9196v.png)
![64=159-3 x^(2) +4x](https://img.qammunity.org/2019/formulas/mathematics/high-school/mpj65jgmkymgkqlh0qd4nc2lsa36dkxjuc.png)
Now you solve the quadratic equation, you'll get a positive and negative value; as this are lengths, you take the positive and get:
![x= (19)/(3)](https://img.qammunity.org/2019/formulas/mathematics/high-school/i0dq7zrlu2n5qm9vlylxrcd2ndvvwvmxf7.png)