A pointed arch which forms isosceles or equilateral triangle, is generally known as

Lancet Arch: A narrow, pointed arch whose radii are greater than its span, forming the shape of an isosceles or equilateral triangle at its apex. It is highly characteristic of Gothic architecture.
Three-centered arch: A broad, flattened arch drawn from three different center points (often used for wider openings like bridges).
Two-centered arch: A general category of pointed arches struck from two centers (a lancet arch is a specific subtype).
Bull's eye arch: A fully circular or oval window/arch, not a pointed one.