The eighth grade of junior high school, the first volume of the class, eye-catching mathematical answers, page 28, 16, 17 answers need to be online urgently. Thank you.
It is proved that triangle ACE and triangle ABD are congruent AC=AB AE=AD, and there is also an angle of 60, so we can get CE=BD and AC+CD =CE, because AC=BC in equilateral triangle. You can ask if you don't know. . .