(5а2-4х+25)+(-31+9а2-3х)= -31+9а2-3х+5а2-4х+25= 14а2-7х-6
(17у+8b2-11)-(70-9b2+18у)= 17у+8b2-11-70+9b2-18у= -у+17b2-81
(2,3с-9,1z2-4)-(10z3-3с+5,9)= 2,3с-9,1z2-4-10z3+3с-5,9= 5,3с-9,1z2-10z3-9,9
(0,8t2-20m+5)-(41-3m-2,4t2)= 0,8t2-20m+5-41+3m+2,4t2= 3,2t2-17m-36