r^2+4r-84=

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Solution for r^2+4r-84= equation:


Simplifying
r2 + 4r + -84 = 0

Reorder the terms:
-84 + 4r + r2 = 0

Solving
-84 + 4r + r2 = 0

Solving for variable 'r'.

Begin completing the square.

Move the constant term to the right:

Add '84' to each side of the equation.
-84 + 4r + 84 + r2 = 0 + 84

Reorder the terms:
-84 + 84 + 4r + r2 = 0 + 84

Combine like terms: -84 + 84 = 0
0 + 4r + r2 = 0 + 84
4r + r2 = 0 + 84

Combine like terms: 0 + 84 = 84
4r + r2 = 84

The r term is 4r.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4r + 4 + r2 = 84 + 4

Reorder the terms:
4 + 4r + r2 = 84 + 4

Combine like terms: 84 + 4 = 88
4 + 4r + r2 = 88

Factor a perfect square on the left side:
(r + 2)(r + 2) = 88

Calculate the square root of the right side: 9.38083152

Break this problem into two subproblems by setting 
(r + 2) equal to 9.38083152 and -9.38083152.

Subproblem 1

r + 2 = 9.38083152 Simplifying r + 2 = 9.38083152 Reorder the terms: 2 + r = 9.38083152 Solving 2 + r = 9.38083152 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + r = 9.38083152 + -2 Combine like terms: 2 + -2 = 0 0 + r = 9.38083152 + -2 r = 9.38083152 + -2 Combine like terms: 9.38083152 + -2 = 7.38083152 r = 7.38083152 Simplifying r = 7.38083152

Subproblem 2

r + 2 = -9.38083152 Simplifying r + 2 = -9.38083152 Reorder the terms: 2 + r = -9.38083152 Solving 2 + r = -9.38083152 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-2' to each side of the equation. 2 + -2 + r = -9.38083152 + -2 Combine like terms: 2 + -2 = 0 0 + r = -9.38083152 + -2 r = -9.38083152 + -2 Combine like terms: -9.38083152 + -2 = -11.38083152 r = -11.38083152 Simplifying r = -11.38083152

Solution

The solution to the problem is based on the solutions from the subproblems. r = {7.38083152, -11.38083152}

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