Question

3. Complete the square for 3x2 - 6x = 21. Help

Answer 1

Answer:

x=1+2√2 or x=1−2√2

Step-by-step explanation:

Let's solve your equation step-by-step.

3x2−6x=21

Step 1: Since the coefficient of 3x^2 is 3, divide both sides by 3.

3x2−6x

3

=

21

3

x2−2x=7

Step 2: The coefficient of -2x is -2. Let b=-2.  

Then we need to add (b/2)^2=1 to both sides to complete the square.

Add 1 to both sides.

x2−2x+1=7+1

x2−2x+1=8

Step 3: Factor left side.

(x−1)2=8

Step 4: Take square root.

x−1=±√8

Step 5: Add 1 to both sides.

x−1+1=1±√8

x=1±√8

x=1+2√2 or x=1−2√2