5r^2-18=2r

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Solution for 5r^2-18=2r equation:


Simplifying
5r2 + -18 = 2r

Reorder the terms:
-18 + 5r2 = 2r

Solving
-18 + 5r2 = 2r

Solving for variable 'r'.

Reorder the terms:
-18 + -2r + 5r2 = 2r + -2r

Combine like terms: 2r + -2r = 0
-18 + -2r + 5r2 = 0

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

Divide each side by '5'.
-3.6 + -0.4r + r2 = 0

Move the constant term to the right:

Add '3.6' to each side of the equation.
-3.6 + -0.4r + 3.6 + r2 = 0 + 3.6

Reorder the terms:
-3.6 + 3.6 + -0.4r + r2 = 0 + 3.6

Combine like terms: -3.6 + 3.6 = 0.0
0.0 + -0.4r + r2 = 0 + 3.6
-0.4r + r2 = 0 + 3.6

Combine like terms: 0 + 3.6 = 3.6
-0.4r + r2 = 3.6

The r term is -0.4r.  Take half its coefficient (-0.2).
Square it (0.04) and add it to both sides.

Add '0.04' to each side of the equation.
-0.4r + 0.04 + r2 = 3.6 + 0.04

Reorder the terms:
0.04 + -0.4r + r2 = 3.6 + 0.04

Combine like terms: 3.6 + 0.04 = 3.64
0.04 + -0.4r + r2 = 3.64

Factor a perfect square on the left side:
(r + -0.2)(r + -0.2) = 3.64

Calculate the square root of the right side: 1.907878403

Break this problem into two subproblems by setting 
(r + -0.2) equal to 1.907878403 and -1.907878403.

Subproblem 1

r + -0.2 = 1.907878403 Simplifying r + -0.2 = 1.907878403 Reorder the terms: -0.2 + r = 1.907878403 Solving -0.2 + r = 1.907878403 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.2' to each side of the equation. -0.2 + 0.2 + r = 1.907878403 + 0.2 Combine like terms: -0.2 + 0.2 = 0.0 0.0 + r = 1.907878403 + 0.2 r = 1.907878403 + 0.2 Combine like terms: 1.907878403 + 0.2 = 2.107878403 r = 2.107878403 Simplifying r = 2.107878403

Subproblem 2

r + -0.2 = -1.907878403 Simplifying r + -0.2 = -1.907878403 Reorder the terms: -0.2 + r = -1.907878403 Solving -0.2 + r = -1.907878403 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.2' to each side of the equation. -0.2 + 0.2 + r = -1.907878403 + 0.2 Combine like terms: -0.2 + 0.2 = 0.0 0.0 + r = -1.907878403 + 0.2 r = -1.907878403 + 0.2 Combine like terms: -1.907878403 + 0.2 = -1.707878403 r = -1.707878403 Simplifying r = -1.707878403

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.107878403, -1.707878403}

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