0=-0.4x^2+16x+90

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Solution for 0=-0.4x^2+16x+90 equation:


Simplifying
0 = -0.4x2 + 16x + 90

Reorder the terms:
0 = 90 + 16x + -0.4x2

Solving
0 = 90 + 16x + -0.4x2

Solving for variable 'x'.

Combine like terms: 0 + -90 = -90
-90 + -16x + 0.4x2 = 90 + 16x + -0.4x2 + -90 + -16x + 0.4x2

Reorder the terms:
-90 + -16x + 0.4x2 = 90 + -90 + 16x + -16x + -0.4x2 + 0.4x2

Combine like terms: 90 + -90 = 0
-90 + -16x + 0.4x2 = 0 + 16x + -16x + -0.4x2 + 0.4x2
-90 + -16x + 0.4x2 = 16x + -16x + -0.4x2 + 0.4x2

Combine like terms: 16x + -16x = 0
-90 + -16x + 0.4x2 = 0 + -0.4x2 + 0.4x2
-90 + -16x + 0.4x2 = -0.4x2 + 0.4x2

Combine like terms: -0.4x2 + 0.4x2 = 0.0
-90 + -16x + 0.4x2 = 0.0

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

Divide each side by '0.4'.
-225 + -40x + x2 = 0

Move the constant term to the right:

Add '225' to each side of the equation.
-225 + -40x + 225 + x2 = 0 + 225

Reorder the terms:
-225 + 225 + -40x + x2 = 0 + 225

Combine like terms: -225 + 225 = 0
0 + -40x + x2 = 0 + 225
-40x + x2 = 0 + 225

Combine like terms: 0 + 225 = 225
-40x + x2 = 225

The x term is -40x.  Take half its coefficient (-20).
Square it (400) and add it to both sides.

Add '400' to each side of the equation.
-40x + 400 + x2 = 225 + 400

Reorder the terms:
400 + -40x + x2 = 225 + 400

Combine like terms: 225 + 400 = 625
400 + -40x + x2 = 625

Factor a perfect square on the left side:
(x + -20)(x + -20) = 625

Calculate the square root of the right side: 25

Break this problem into two subproblems by setting 
(x + -20) equal to 25 and -25.

Subproblem 1

x + -20 = 25 Simplifying x + -20 = 25 Reorder the terms: -20 + x = 25 Solving -20 + x = 25 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '20' to each side of the equation. -20 + 20 + x = 25 + 20 Combine like terms: -20 + 20 = 0 0 + x = 25 + 20 x = 25 + 20 Combine like terms: 25 + 20 = 45 x = 45 Simplifying x = 45

Subproblem 2

x + -20 = -25 Simplifying x + -20 = -25 Reorder the terms: -20 + x = -25 Solving -20 + x = -25 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '20' to each side of the equation. -20 + 20 + x = -25 + 20 Combine like terms: -20 + 20 = 0 0 + x = -25 + 20 x = -25 + 20 Combine like terms: -25 + 20 = -5 x = -5 Simplifying x = -5

Solution

The solution to the problem is based on the solutions from the subproblems. x = {45, -5}

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