Answer:
10
Explanation:
The triangle angle bisector theorem states that an angle bisector of an angle of a triangle divides the opposite side in two segments that are proportional to the other two sides of the triangle.
This means the proportion of the two given sides of ABC, 8/12, is the same as the proportion of the segments that make up BC, (x+4)/(2x+1). This gives us the proportion
8/12 = (x+4)/(2x+1)
Cross multiplying,
8(2x+1) = 12(x+4)
Using the distributive property,
8(2x)+8(1) = 12(x)+12(4)
16x+8 = 12x+48
Subtract 12x from each side:
16x+8-12x = 12x+48-12x
4x+8 = 48
Subtract 8 from each side:
4x+8-8 = 48-8
4x = 40
Divide both sides by 4:
4x/4 = 40/4
x = 10