Question

If a+b+c=7, ab+bc+ac=21, a^2+b^2+c^2=?​

Answer 1

Answer:

7

${x}^{2} + {y}^{2} + {z}^{2} =( x + y + z)^{2} - 2 \times xy + yz + zx \\ so \: 49 - 2 \times 21 = 7$