Question

Solve x2-14x+21=0 by completing the square

Answer 1

`x^2-14x+21=0\\\\x^2-2x\cdot7+7^2-7^2+21=0\\\\(x-7)^2-49+21=0\\\\(x-7)^2-28=0\\\\(x-7)^2=28\iff x-7=-√(28)\ \vee\ x-7=√(28)\\\\x=7-√(4\cdot7)\ \vee\ x=7+√(4\cdot7)\\\\x=7-2\sqrt7\ \vee\ x=7+2\sqrt7`