(z+7)(5z-4)=18

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Solution for (z+7)(5z-4)=18 equation:


Simplifying
(z + 7)(5z + -4) = 18

Reorder the terms:
(7 + z)(5z + -4) = 18

Reorder the terms:
(7 + z)(-4 + 5z) = 18

Multiply (7 + z) * (-4 + 5z)
(7(-4 + 5z) + z(-4 + 5z)) = 18
((-4 * 7 + 5z * 7) + z(-4 + 5z)) = 18
((-28 + 35z) + z(-4 + 5z)) = 18
(-28 + 35z + (-4 * z + 5z * z)) = 18
(-28 + 35z + (-4z + 5z2)) = 18

Combine like terms: 35z + -4z = 31z
(-28 + 31z + 5z2) = 18

Solving
-28 + 31z + 5z2 = 18

Solving for variable 'z'.

Reorder the terms:
-28 + -18 + 31z + 5z2 = 18 + -18

Combine like terms: -28 + -18 = -46
-46 + 31z + 5z2 = 18 + -18

Combine like terms: 18 + -18 = 0
-46 + 31z + 5z2 = 0

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

Divide each side by '5'.
-9.2 + 6.2z + z2 = 0

Move the constant term to the right:

Add '9.2' to each side of the equation.
-9.2 + 6.2z + 9.2 + z2 = 0 + 9.2

Reorder the terms:
-9.2 + 9.2 + 6.2z + z2 = 0 + 9.2

Combine like terms: -9.2 + 9.2 = 0.0
0.0 + 6.2z + z2 = 0 + 9.2
6.2z + z2 = 0 + 9.2

Combine like terms: 0 + 9.2 = 9.2
6.2z + z2 = 9.2

The z term is 6.2z.  Take half its coefficient (3.1).
Square it (9.61) and add it to both sides.

Add '9.61' to each side of the equation.
6.2z + 9.61 + z2 = 9.2 + 9.61

Reorder the terms:
9.61 + 6.2z + z2 = 9.2 + 9.61

Combine like terms: 9.2 + 9.61 = 18.81
9.61 + 6.2z + z2 = 18.81

Factor a perfect square on the left side:
(z + 3.1)(z + 3.1) = 18.81

Calculate the square root of the right side: 4.337049688

Break this problem into two subproblems by setting 
(z + 3.1) equal to 4.337049688 and -4.337049688.

Subproblem 1

z + 3.1 = 4.337049688 Simplifying z + 3.1 = 4.337049688 Reorder the terms: 3.1 + z = 4.337049688 Solving 3.1 + z = 4.337049688 Solving for variable 'z'. Move all terms containing z to the left, all other terms to the right. Add '-3.1' to each side of the equation. 3.1 + -3.1 + z = 4.337049688 + -3.1 Combine like terms: 3.1 + -3.1 = 0.0 0.0 + z = 4.337049688 + -3.1 z = 4.337049688 + -3.1 Combine like terms: 4.337049688 + -3.1 = 1.237049688 z = 1.237049688 Simplifying z = 1.237049688

Subproblem 2

z + 3.1 = -4.337049688 Simplifying z + 3.1 = -4.337049688 Reorder the terms: 3.1 + z = -4.337049688 Solving 3.1 + z = -4.337049688 Solving for variable 'z'. Move all terms containing z to the left, all other terms to the right. Add '-3.1' to each side of the equation. 3.1 + -3.1 + z = -4.337049688 + -3.1 Combine like terms: 3.1 + -3.1 = 0.0 0.0 + z = -4.337049688 + -3.1 z = -4.337049688 + -3.1 Combine like terms: -4.337049688 + -3.1 = -7.437049688 z = -7.437049688 Simplifying z = -7.437049688

Solution

The solution to the problem is based on the solutions from the subproblems. z = {1.237049688, -7.437049688}

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