x^2+2x=400

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Solution for x^2+2x=400 equation:


Simplifying
x2 + 2x = 400

Reorder the terms:
2x + x2 = 400

Solving
2x + x2 = 400

Solving for variable 'x'.

Reorder the terms:
-400 + 2x + x2 = 400 + -400

Combine like terms: 400 + -400 = 0
-400 + 2x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '400' to each side of the equation.
-400 + 2x + 400 + x2 = 0 + 400

Reorder the terms:
-400 + 400 + 2x + x2 = 0 + 400

Combine like terms: -400 + 400 = 0
0 + 2x + x2 = 0 + 400
2x + x2 = 0 + 400

Combine like terms: 0 + 400 = 400
2x + x2 = 400

The x term is 2x.  Take half its coefficient (1).
Square it (1) and add it to both sides.

Add '1' to each side of the equation.
2x + 1 + x2 = 400 + 1

Reorder the terms:
1 + 2x + x2 = 400 + 1

Combine like terms: 400 + 1 = 401
1 + 2x + x2 = 401

Factor a perfect square on the left side:
(x + 1)(x + 1) = 401

Calculate the square root of the right side: 20.024984395

Break this problem into two subproblems by setting 
(x + 1) equal to 20.024984395 and -20.024984395.

Subproblem 1

x + 1 = 20.024984395 Simplifying x + 1 = 20.024984395 Reorder the terms: 1 + x = 20.024984395 Solving 1 + x = 20.024984395 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + x = 20.024984395 + -1 Combine like terms: 1 + -1 = 0 0 + x = 20.024984395 + -1 x = 20.024984395 + -1 Combine like terms: 20.024984395 + -1 = 19.024984395 x = 19.024984395 Simplifying x = 19.024984395

Subproblem 2

x + 1 = -20.024984395 Simplifying x + 1 = -20.024984395 Reorder the terms: 1 + x = -20.024984395 Solving 1 + x = -20.024984395 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-1' to each side of the equation. 1 + -1 + x = -20.024984395 + -1 Combine like terms: 1 + -1 = 0 0 + x = -20.024984395 + -1 x = -20.024984395 + -1 Combine like terms: -20.024984395 + -1 = -21.024984395 x = -21.024984395 Simplifying x = -21.024984395

Solution

The solution to the problem is based on the solutions from the subproblems. x = {19.024984395, -21.024984395}

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