1.
4(p+c)=40⇒p+c=40:4,⇒p+c=10⇒p=10-c
5p+6c=56⇒5(10-c)+6c=56⇒50-5c+6c=56⇒c=56-50⇒c=6
p=10-c=10-6=4⇒caini=6, pisici =4
2.(a-b)/(a+b)=2/3
3(a-b)=2(a+b)⇒3a-3b=2a+2b⇒3a-2a=2b+3b
a=5b
(2022·a-100·b)/(2000·a+15b)=
(2022·5b-100·b)/(2000·5b+15b)=[b(10110-100)]/b·(10000+15)=10010:10015
= 2002:2003 = 0,99950074
3.[tex]n^{4}+ n^{2} +1=(n^{2}+1)^{2})-n^{2}=(n^{2}+n+1)(n^{2}-n+1)=[/tex]
