x^2-4x=81

Simple and best practice solution for x^2-4x=81 equation. Check how easy it is, and learn it for the future. Our solution is simple, and easy to understand, so don`t hesitate to use it as a solution of your homework.

If it's not what You are looking for type in the equation solver your own equation and let us solve it.

Solution for x^2-4x=81 equation:


Simplifying
x2 + -4x = 81

Reorder the terms:
-4x + x2 = 81

Solving
-4x + x2 = 81

Solving for variable 'x'.

Reorder the terms:
-81 + -4x + x2 = 81 + -81

Combine like terms: 81 + -81 = 0
-81 + -4x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '81' to each side of the equation.
-81 + -4x + 81 + x2 = 0 + 81

Reorder the terms:
-81 + 81 + -4x + x2 = 0 + 81

Combine like terms: -81 + 81 = 0
0 + -4x + x2 = 0 + 81
-4x + x2 = 0 + 81

Combine like terms: 0 + 81 = 81
-4x + x2 = 81

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

Add '4' to each side of the equation.
-4x + 4 + x2 = 81 + 4

Reorder the terms:
4 + -4x + x2 = 81 + 4

Combine like terms: 81 + 4 = 85
4 + -4x + x2 = 85

Factor a perfect square on the left side:
(x + -2)(x + -2) = 85

Calculate the square root of the right side: 9.219544457

Break this problem into two subproblems by setting 
(x + -2) equal to 9.219544457 and -9.219544457.

Subproblem 1

x + -2 = 9.219544457 Simplifying x + -2 = 9.219544457 Reorder the terms: -2 + x = 9.219544457 Solving -2 + x = 9.219544457 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + x = 9.219544457 + 2 Combine like terms: -2 + 2 = 0 0 + x = 9.219544457 + 2 x = 9.219544457 + 2 Combine like terms: 9.219544457 + 2 = 11.219544457 x = 11.219544457 Simplifying x = 11.219544457

Subproblem 2

x + -2 = -9.219544457 Simplifying x + -2 = -9.219544457 Reorder the terms: -2 + x = -9.219544457 Solving -2 + x = -9.219544457 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '2' to each side of the equation. -2 + 2 + x = -9.219544457 + 2 Combine like terms: -2 + 2 = 0 0 + x = -9.219544457 + 2 x = -9.219544457 + 2 Combine like terms: -9.219544457 + 2 = -7.219544457 x = -7.219544457 Simplifying x = -7.219544457

Solution

The solution to the problem is based on the solutions from the subproblems. x = {11.219544457, -7.219544457}

See similar equations:

| -3x-3y=-30 | | -19=-5(0)+b | | -3x-8=-9 | | 2(n+1/3)=3/2n+1+1/2n-1/3 | | -x^2+2x=2 | | -45-10=10x+15 | | 9x^2+3kx+4=0 | | (y-29)+45=76 | | 11/9/19/9 | | -6(2r+8)=-12 | | 5x^2+9x=-x^2+5x+1 | | 3(5x+3)=69 | | 2x^2+8x=234 | | t-6t-16=0 | | 6t^2+36t=0 | | 2x^2+1=17 | | 5.5+3y=5 | | -a1/2+12=-9 | | -19=2x | | 25-9n^2=0 | | (20+x)/5y=2y/x | | 2/3h-9=6-2/3h | | 7(d-5)+8=(3d-8)+1 | | 20+x=2y | | -5y-(-7)=52 | | 3x+16=10x+61 | | -1/5y=10 | | X^2/25-6=-2 | | 40-4x=9x-1 | | -15.6+32.8= | | 74=55*n | | 6=2m+3 |

Equations solver categories