4r(r-1)=19

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Solution for 4r(r-1)=19 equation:


Simplifying
4r(r + -1) = 19

Reorder the terms:
4r(-1 + r) = 19
(-1 * 4r + r * 4r) = 19
(-4r + 4r2) = 19

Solving
-4r + 4r2 = 19

Solving for variable 'r'.

Reorder the terms:
-19 + -4r + 4r2 = 19 + -19

Combine like terms: 19 + -19 = 0
-19 + -4r + 4r2 = 0

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

Divide each side by '4'.
-4.75 + -1r + r2 = 0

Move the constant term to the right:

Add '4.75' to each side of the equation.
-4.75 + -1r + 4.75 + r2 = 0 + 4.75

Reorder the terms:
-4.75 + 4.75 + -1r + r2 = 0 + 4.75

Combine like terms: -4.75 + 4.75 = 0.00
0.00 + -1r + r2 = 0 + 4.75
-1r + r2 = 0 + 4.75

Combine like terms: 0 + 4.75 = 4.75
-1r + r2 = 4.75

The r term is -1r.  Take half its coefficient (-0.5).
Square it (0.25) and add it to both sides.

Add '0.25' to each side of the equation.
-1r + 0.25 + r2 = 4.75 + 0.25

Reorder the terms:
0.25 + -1r + r2 = 4.75 + 0.25

Combine like terms: 4.75 + 0.25 = 5
0.25 + -1r + r2 = 5

Factor a perfect square on the left side:
(r + -0.5)(r + -0.5) = 5

Calculate the square root of the right side: 2.236067978

Break this problem into two subproblems by setting 
(r + -0.5) equal to 2.236067978 and -2.236067978.

Subproblem 1

r + -0.5 = 2.236067978 Simplifying r + -0.5 = 2.236067978 Reorder the terms: -0.5 + r = 2.236067978 Solving -0.5 + r = 2.236067978 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = 2.236067978 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = 2.236067978 + 0.5 r = 2.236067978 + 0.5 Combine like terms: 2.236067978 + 0.5 = 2.736067978 r = 2.736067978 Simplifying r = 2.736067978

Subproblem 2

r + -0.5 = -2.236067978 Simplifying r + -0.5 = -2.236067978 Reorder the terms: -0.5 + r = -2.236067978 Solving -0.5 + r = -2.236067978 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '0.5' to each side of the equation. -0.5 + 0.5 + r = -2.236067978 + 0.5 Combine like terms: -0.5 + 0.5 = 0.0 0.0 + r = -2.236067978 + 0.5 r = -2.236067978 + 0.5 Combine like terms: -2.236067978 + 0.5 = -1.736067978 r = -1.736067978 Simplifying r = -1.736067978

Solution

The solution to the problem is based on the solutions from the subproblems. r = {2.736067978, -1.736067978}

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