Решение 

AC = `*`(AB, `*`(cos, `*`(A))) 

`and`(AC = `+`(`*`(17, `*`(sqrt(`+`(1, `-`(`^`(`/`(8, 17), 2))))))), `and`(`+`(`*`(17, `*`(sqrt(`+`(1, `-`(`^`(`/`(8, 17), 2))))))) = sqrt(`+`(`^`(17, 2), `-`(`^`(8, 2)))), `and`(sqrt(`+`(`^`(17, 2), ...