x^2+7x=400

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Solution for x^2+7x=400 equation:


Simplifying
x2 + 7x = 400

Reorder the terms:
7x + x2 = 400

Solving
7x + x2 = 400

Solving for variable 'x'.

Reorder the terms:
-400 + 7x + x2 = 400 + -400

Combine like terms: 400 + -400 = 0
-400 + 7x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '400' to each side of the equation.
-400 + 7x + 400 + x2 = 0 + 400

Reorder the terms:
-400 + 400 + 7x + x2 = 0 + 400

Combine like terms: -400 + 400 = 0
0 + 7x + x2 = 0 + 400
7x + x2 = 0 + 400

Combine like terms: 0 + 400 = 400
7x + x2 = 400

The x term is 7x.  Take half its coefficient (3.5).
Square it (12.25) and add it to both sides.

Add '12.25' to each side of the equation.
7x + 12.25 + x2 = 400 + 12.25

Reorder the terms:
12.25 + 7x + x2 = 400 + 12.25

Combine like terms: 400 + 12.25 = 412.25
12.25 + 7x + x2 = 412.25

Factor a perfect square on the left side:
(x + 3.5)(x + 3.5) = 412.25

Calculate the square root of the right side: 20.303940504

Break this problem into two subproblems by setting 
(x + 3.5) equal to 20.303940504 and -20.303940504.

Subproblem 1

x + 3.5 = 20.303940504 Simplifying x + 3.5 = 20.303940504 Reorder the terms: 3.5 + x = 20.303940504 Solving 3.5 + x = 20.303940504 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.5' to each side of the equation. 3.5 + -3.5 + x = 20.303940504 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = 20.303940504 + -3.5 x = 20.303940504 + -3.5 Combine like terms: 20.303940504 + -3.5 = 16.803940504 x = 16.803940504 Simplifying x = 16.803940504

Subproblem 2

x + 3.5 = -20.303940504 Simplifying x + 3.5 = -20.303940504 Reorder the terms: 3.5 + x = -20.303940504 Solving 3.5 + x = -20.303940504 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '-3.5' to each side of the equation. 3.5 + -3.5 + x = -20.303940504 + -3.5 Combine like terms: 3.5 + -3.5 = 0.0 0.0 + x = -20.303940504 + -3.5 x = -20.303940504 + -3.5 Combine like terms: -20.303940504 + -3.5 = -23.803940504 x = -23.803940504 Simplifying x = -23.803940504

Solution

The solution to the problem is based on the solutions from the subproblems. x = {16.803940504, -23.803940504}

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