# Length of the Latus Rectum

The latus rectum of a parabola is the chord passing through the focus and perpendicular to the axis.

In other words the focal chord perpendicular to the axis of a parabola is the called the latus rectum of the parabola.

**Length of the Latus Rectum**

Recall latus rectum is the chord of the parabola passing through the focus and perpendicular to the axis of the parabola. In figure given below, BFB' is the latus rectum.

Now, BFB' = 2FB

The coordinates of B are (a, BF).

Since B lies on the parabola, we must have

BF

^{2 }= 4a.a

â‡’ BF = 2a.

â‡’ BFB' = 4a, which is the length of latus rectum.