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Find the answers to the after-school exercises on page 2- 1 92 of senior high school mathematics elective course (detailed process)
Vector AB 1 times vector BC1= (AB+AA1) * (BC+BB1) = AB * BC+AA1* BC+AA1* BB/kloc.
AB * BC =/AB//BC/cos 120 =- 1 aa 1 * BC = 0 aa 1 * bb 1 = 1 AB * bb 1 = 0
So the above formula =0, so the included angle is 90 degrees.
The included angle between two complementary straight lines is 0~90 degrees.