证明：a²+b+²c²+2ab+2bc+2ca=（a+b+c）²

证明：a²+b+²c²+2ab+2bc+2ca=（a+b+c）²
证明：a²+b+²c²+2ab+2bc+2ca=（a+b+c）²

证明：a²+b+²c²+2ab+2bc+2ca=（a+b+c）²
a²+b+²c²+2ab+2bc+2ca
=a²+2ab+b² + 2bc+2ca + c²
=(a+b)² + 2c(a+b) + c²
=(a+b+c)²

移项做差。左边减右边的，等于零不就行了吗

（a+b+c）²=a²+2a(b+c)+(b+c）²=a²+2ab+2ca+b+²c²+2bc=a²+b+²c²+2ab+2bc+2ca