x^2-3x=21

Simple and best practice solution for x^2-3x=21 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^2-3x=21 equation:


Simplifying
x2 + -3x = 21

Reorder the terms:
-3x + x2 = 21

Solving
-3x + x2 = 21

Solving for variable 'x'.

Reorder the terms:
-21 + -3x + x2 = 21 + -21

Combine like terms: 21 + -21 = 0
-21 + -3x + x2 = 0

Begin completing the square.

Move the constant term to the right:

Add '21' to each side of the equation.
-21 + -3x + 21 + x2 = 0 + 21

Reorder the terms:
-21 + 21 + -3x + x2 = 0 + 21

Combine like terms: -21 + 21 = 0
0 + -3x + x2 = 0 + 21
-3x + x2 = 0 + 21

Combine like terms: 0 + 21 = 21
-3x + x2 = 21

The x term is -3x.  Take half its coefficient (-1.5).
Square it (2.25) and add it to both sides.

Add '2.25' to each side of the equation.
-3x + 2.25 + x2 = 21 + 2.25

Reorder the terms:
2.25 + -3x + x2 = 21 + 2.25

Combine like terms: 21 + 2.25 = 23.25
2.25 + -3x + x2 = 23.25

Factor a perfect square on the left side:
(x + -1.5)(x + -1.5) = 23.25

Calculate the square root of the right side: 4.82182538

Break this problem into two subproblems by setting 
(x + -1.5) equal to 4.82182538 and -4.82182538.

Subproblem 1

x + -1.5 = 4.82182538 Simplifying x + -1.5 = 4.82182538 Reorder the terms: -1.5 + x = 4.82182538 Solving -1.5 + x = 4.82182538 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + x = 4.82182538 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = 4.82182538 + 1.5 x = 4.82182538 + 1.5 Combine like terms: 4.82182538 + 1.5 = 6.32182538 x = 6.32182538 Simplifying x = 6.32182538

Subproblem 2

x + -1.5 = -4.82182538 Simplifying x + -1.5 = -4.82182538 Reorder the terms: -1.5 + x = -4.82182538 Solving -1.5 + x = -4.82182538 Solving for variable 'x'. Move all terms containing x to the left, all other terms to the right. Add '1.5' to each side of the equation. -1.5 + 1.5 + x = -4.82182538 + 1.5 Combine like terms: -1.5 + 1.5 = 0.0 0.0 + x = -4.82182538 + 1.5 x = -4.82182538 + 1.5 Combine like terms: -4.82182538 + 1.5 = -3.32182538 x = -3.32182538 Simplifying x = -3.32182538

Solution

The solution to the problem is based on the solutions from the subproblems. x = {6.32182538, -3.32182538}

See similar equations:

| 2(6r^2+4r)= | | 2(3x+5)-3(4x+6)+8(x-1)=30 | | 6x-2,3=8,5 | | 7x+6y=114 | | 4x^2*5x=2 | | 4*tanx+15=0 | | 14qt=l | | -0.06x^2+1.2x+28=0 | | 3x^2+3y^2+24x+6y-24=0 | | 4a(9*6)= | | ax+bx=k-60b | | 12x-60=90 | | (x-7)=(x^2-49) | | ax+bx=k | | (2y-15)=(3y+4y^2) | | ax+b(x+60)=k | | 5p-7=-28 | | ax+bx-60b=0 | | (2x-3y)*(2x+3y)= | | (x^2+3x)=(x^2-xy) | | 14-0=-40 | | y(x+1)dx+(x+1)dy=0 | | 6m^2-23m+20= | | 20x^2+25x-1000=0 | | 56k-24=-4k-8 | | 8x+1=3x+7 | | 60k=32 | | Y=A+A*B | | Psquared-8p+16= | | 4x^3-108x=0 | | 60+8y=-4y | | y=cot(3x^2+5) |

Equations solver categories