А) (с-7)*(с+2)=(с²+2c)-(7c+14)=c²+2c-7c-14=с²-5с-14
б) (5с+2)*(1-2с)=(5с-10с²)+(2-4с)=5с-10с²+2-4с=с-10с²+2
в) (3c-2d)(d-c)=(3cd-3c²)-(2d²-2cd)= 3cd-3c²-2d²-2cd=cd-3c²-2d²
г) (a+b)(3a-b+2)=3a²-ab+2a+3ab-b²+2b=3a²+2ab+2a-b²+2b
д) (х²+1)(4-х²)=4х²-х^4+4-х²=3х²-х^4+4
е)(5-х)(5+х)=(25+5х)-(5х+х²)=25+5х-5х-х²=25-х²