x = 8
Solution:
Side-splitter theorem:
<em>If a line is parallel to one side of a triangle and the line intersects the other two sides, then this line divides those two sides proportionally.</em>
Do cross multiplication, we get
⇒ 4 × 42 = 21x
Divide by 21 on both sides, we get
⇒ 4 × 2 = x
⇒ 8 = x
Switch the sides.
⇒ x = 8
The value of x is 8.