Not far to the west of Cassiopeia, there are four stars forming a triangle, which is about three stars in a line. What constellation is this?

I can't give the landlord a definite answer to this question. "West of Cassiopeia" and "Four stars form a triangle and three stars are in a straight line" are somewhat vague.

But the brightest place in the autumn sky is south of Cassiopeia (from the equatorial coordinate system), so I intercepted this sky area on Stellarium for the landlord's reference:

Two possible candidate combinations are given. The first one is Perseus. I circled the main star of Perseus, Tianzhou III, plus the left and right two Tianzhou II and IV (both third-class) and Daling V in the southwest, forming a figure that basically meets the requirements of the landlord.

Another possibility is to look for Andromeda (the lower left corner of the picture), whose four bright stars are arranged in a straight line approximately, and then look for a triangle (3.5, etc. , the triangle in the left) or a constellation in Aries (2 stars, the constellation in the upper left is not truncated), which also meets the requirements of the landlord.

The description of PS Cassiopeia is very subtle ~ If you are interested, you may wish to use Stellarium to open the coordinate system and ponder it (except the North Pole direction, the other three directions can be substituted, but they are not suitable).