Разложите на множители (c+19d)^2−(19c+d)^2

(c + 19d - (19c + d))(c + 19d + 19c + d)=  
= (c + 19d - 19c - d)(20d + 20c) = 
= (18d - 18c)(20d + 20c) = 
= 360(d - c)(d + c) 

Вот держи.....
(c+19d)^2-(19c+d)^2=(c + 19d - (19c + d))(c + 19d + 19c + d)=
= (c + 19d - 19c - d)(20d + 20c) =
= (18d - 18c)(20d + 20c) =
= 360(d - c)(d + c) ......