From point A to the alpha plane, AA1 is perpendicular and AB is inclined. BA1 projection oblique.

From point A to the alpha plane, AA1 is perpendicular and AB is inclined. BA1 projection oblique. Find: BA1 if AB = 5cm. , AA1 = 4cm.

Since AA1, by condition, is perpendicular to the plane α, and the projection of A1B is inclined AB onto this plane, then the segment AA1 is perpendicular to the projection A1B, and then triangle AA1B is rectangular.

In a right-angled triangle АА1В, according to the Pythagorean theorem, we determine the length of the leg А1В.

A1B ^ 2 = AB ^ 2 – AA1 ^ 2 = 25 – 16 = 9.

A1B = 3 cm.

Answer: The projection length of A1B is 3 cm.