Simplify:
(a−2b+5c)(a−b)−(a−b−c)(2a+3c)+(6a+b)(2c−3a−5b)
(a−2b+5c)(a−b)−(a−b−c)(2a+3c)+(6a+b)(2c−3a−5b)=[a2−ab−2ab+2b2+5ac−5bc]−[2a2+3ac−2ab−3bc−2ac−3c2]+[12ac−18a2−30ab+2bc−3ab−5b2]=a2−ab−2ab+2b2+5ac−5bc−2a2−3ac+2ab+3bc+2ac+3c2+12ac−18a2−30ab+2bc−3ab−5b2=a2−2a2−18a2+2b2−5b2+3c2−ab−30ab−3ab+5ac−3ac+2ac+12ac−5bc+3bc+2bc=−19a2−3b2+3c2−34ab+16acAns.