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demonstrati ca: (a+b+c)²=a²+b²+c²+2ab+2bc²2ca

Răspuns :

aplici formula (a+b+c)² = a² + b² + c² +2ab+ 2ac + 2bc

(a+b+c)²=(a+b+c)(a+b+c)=a²+ab+ac+ab+b²+bc+ac+bc+c²=a²+b²+c²+2ab+2ac+2bc
Deci doar desfaci parantezele.