(b-d)/(a-d)＜(b-c)/(a-c)＜b/a＜(b+c)/(a+c)＜(b+d)/(a+d) - b(a+c) ab+bc bc b - (b+c)(a+d) ab+bd+ac+cd ac+bd b(d-c) 0 c - if 0 (b-c)a -ac a > b OK - 0 c - if a-c (b-c)a > b(a-c) -ac > -bc a - if 0 (b-d)(a-c) ab-ad-bc+cd -ad-bc a(c-d) c-d c -…