Respostas

2013-07-11T20:32:30-03:00
(a+b)² = a² + 2ab + b², logo= a²+ b² + 2ab = 15 + 16= 31 
3ab= 3.8 = 24

31-24= 7
2013-07-11T20:35:41-03:00
(a+b)²-3ab
(a²+2ab+b²)-3ab
(15+2.8)-3.8
(15+16)-24
31-24
7
espero ter ajudado!!!!!