Use the side-splitter theorem to solve for x in the triangle below.
21
42

x = 8

Solution:

Side-splitter theorem:

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.

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.