In the triangular prism abc-a1b1c1, ab = AC = 2aa1, ∠ baa1 = ∠ caa1 = 60 °, D and E are the midpoint of AB and A1C respectively

In the triangular prism abc-a1b1c1, ab = AC = 2aa1, ∠ baa1 = ∠ caa1 = 60 °, D and E are the midpoint of AB and A1C respectively

Let Aa1 = 1, ab = AC = 2, in triangle a1ab, < a1ab = 60 °, according to cosine theorem, A1B = √ 3, Aa1 ^ 2 + A1B ^ 2 = 4, AB ^ 2 = 4, according to Pythagorean inverse theorem, △ a1ab is RT △ and < aa1b = < b1ba1 = 90 °, then BB1 ⊥ A1B, similarly, < aa1c = 90 °, Aa1 ⊥ A1C, BB1 / / Aa1, then BB1 ⊥ A1C, A1C ∩ A1B = a

Elden Ring Premiere

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