(a-1)(b+c)-(a-1)(b-c)

(a-1)(b+c)-(a-1)(b-c) = = ab+ac-b-c-(ab-ac-b+c) = = ab+ac-b-c-ab+ac+b-c = = 2ac-2c = 2c(a-1)

(a-1)(b+c)-(a-1)(b-c) = = ab+ac-b-c-ab+ac+b-c = = 2ac-2c = 2c(a-1) mysle że pomogłam ;p;p

(a-1)(b+c)-(a-1)(b-c)= ab+ac-b-c-(ab-ac-b+c)=ab+ac-b-c-ab+ac+b-c=2ac-2c=2c(a-1)