Question

Solve x2 = 12x – 15 by completing the square. Which is the solution set of the equation? Solve x2 = 12x – 15 by completing the square. Which is the solution set of the equation?

Answer 1

Answer:

D on edge

Step-by-step explanation:

Answer 2

Answer: $6+\sqrt{21}\ \text{and}\ 6-\sqrt{21}$

Step-by-step explanation:

Given

Quadratic equation is

$x^2-12x+15=0$

Solving by completing the square method

$\Rightarrow x^2-2\cdot 6\cdot x+15=0\\\text{add and subtract 36}\\\Rightarrow x^2-2\cdot 6\cdot x+15+36-36=0\\\Rightarrow x^2-2\cdot 6\cdot x+36+(-36+15)=0\\\text{using}\ (a-b)^2=a^2+b^2-2ab\\\Rightarrow (x-6)^2-21=0\\\Rightarrow (x-6)^2=21\\\Rightarrow x-6=\pm \sqrt{21}\\\Rightarrow x=6\pm \sqrt{21}$

The solution set of the equation is $6+\sqrt{21}\ \text{and}\ 6-\sqrt{21}$