The side length of square ABCD is a, PA ⊥ plane ABCD, PA = a, m, n are the midpoint of PD, Pb respectively, then the cosine value of the angle formed by the line am and cn is
Let me try... Two methods are given, I hope LZ can add points to connect dB, make AE / / DB through a, cross CB extension line to e, take the midpoint of AE F, connect NF, Mn ∵ m, n are the midpoint of PD, Pb ∵ Mn / / = 1 / 2bd ∵ AF = 1 / 2ae / / = 1 / 2bd ∵ Mn / / = AF ∵ mnfa is parallelogram ∵ AM / / = FN, the angle between line am and CN