3=-0.01x^2-0.3x+21

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Solution for 3=-0.01x^2-0.3x+21 equation:


Simplifying
3 = -0.01x2 + -0.3x + 21

Reorder the terms:
3 = 21 + -0.3x + -0.01x2

Solving
3 = 21 + -0.3x + -0.01x2

Solving for variable 'x'.

Combine like terms: 3 + -21 = -18
-18 + 0.3x + 0.01x2 = 21 + -0.3x + -0.01x2 + -21 + 0.3x + 0.01x2

Reorder the terms:
-18 + 0.3x + 0.01x2 = 21 + -21 + -0.3x + 0.3x + -0.01x2 + 0.01x2

Combine like terms: 21 + -21 = 0
-18 + 0.3x + 0.01x2 = 0 + -0.3x + 0.3x + -0.01x2 + 0.01x2
-18 + 0.3x + 0.01x2 = -0.3x + 0.3x + -0.01x2 + 0.01x2

Combine like terms: -0.3x + 0.3x = 0.0
-18 + 0.3x + 0.01x2 = 0.0 + -0.01x2 + 0.01x2
-18 + 0.3x + 0.01x2 = -0.01x2 + 0.01x2

Combine like terms: -0.01x2 + 0.01x2 = 0.00
-18 + 0.3x + 0.01x2 = 0.00

Begin completing the square.  Divide all terms by
0.01 the coefficient of the squared term: 

Divide each side by '0.01'.
-1800 + 30x + x2 = 0

Move the constant term to the right:

Add '1800' to each side of the equation.
-1800 + 30x + 1800 + x2 = 0 + 1800

Reorder the terms:
-1800 + 1800 + 30x + x2 = 0 + 1800

Combine like terms: -1800 + 1800 = 0
0 + 30x + x2 = 0 + 1800
30x + x2 = 0 + 1800

Combine like terms: 0 + 1800 = 1800
30x + x2 = 1800

The x term is 30x.  Take half its coefficient (15).
Square it (225) and add it to both sides.

Add '225' to each side of the equation.
30x + 225 + x2 = 1800 + 225

Reorder the terms:
225 + 30x + x2 = 1800 + 225

Combine like terms: 1800 + 225 = 2025
225 + 30x + x2 = 2025

Factor a perfect square on the left side:
(x + 15)(x + 15) = 2025

Calculate the square root of the right side: 45

Break this problem into two subproblems by setting 
(x + 15) equal to 45 and -45.

Subproblem 1

x + 15 = 45 Simplifying x + 15 = 45 Reorder the terms: 15 + x = 45 Solving 15 + x = 45 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-15' to each side of the equation. 15 + -15 + x = 45 + -15 Combine like terms: 15 + -15 = 0 0 + x = 45 + -15 x = 45 + -15 Combine like terms: 45 + -15 = 30 x = 30 Simplifying x = 30

Subproblem 2

x + 15 = -45 Simplifying x + 15 = -45 Reorder the terms: 15 + x = -45 Solving 15 + x = -45 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-15' to each side of the equation. 15 + -15 + x = -45 + -15 Combine like terms: 15 + -15 = 0 0 + x = -45 + -15 x = -45 + -15 Combine like terms: -45 + -15 = -60 x = -60 Simplifying x = -60

Solution

The solution to the problem is based on the solutions from the subproblems. x = {30, -60}

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