Question

To solve the equation below by completing the square, what is your first step?

3x2 + 18x = 21

Add 9 to each side of the equation.

Divide both sides of the equation by 3

Multiply both sides of the equation by 3

Add 81 to each side of the equation.

Answer 1

Answer:

The first step to solve the equation by completing the square 3x²+ 18x= 21 is multiply both sides of the equation by .

The factors of the equations 3x²+ 18x= 21 are 1 ,-7 .

Explanation:

As given the equations

3x² + 18x = 21

Multiply both sides of the equation by .

Thus the equation becomes

Simplify the above

x² + 6x = 7

Adding 9 on both sides of the above equation

x² + 6x + 9 = 7 + 9

x² + 6x + 9 = 16

(As (a +b)² = a² + b² + 2ab

Thus (x+3)² = x² + 6x + 9 )

Put in the above

(x+3)² = 16

Taking square root on both side

√16 = ± 4

First take

(x + 3) = 4

x = 4 -3

x = 1

Second take

(x+ 3) = -4

x = - 4 -3

x = -7

Therefore the first step to solve the equation by completing the square 3x²+ 18x= 21 is multiply both sides of the equation by .

The factors of the equations 3x²+ 18x= 21 are 1 ,-7 .

Answer 2

Explanation:

well, for that I want the equation as simple a possible. especially do I want to have a pure "x²" term with "1" as the factor.

so, as I see that all terms in the equation are multiples of 3, my first step will be to divide both sides by 3.

leading to

x² + 6x = 7