Question

solve using the quadratic formula x^2=4x+21

Answer 1

Simplifying
x2 = 4x + 21

Reorder the terms:
x2 = 21 + 4x

Solving
x2 = 21 + 4x

Solving for variable 'x'.

Reorder the terms:
-21 + -4x + x2 = 21 + 4x + -21 + -4x

Reorder the terms:
-21 + -4x + x2 = 21 + -21 + 4x + -4x

Combine like terms: 21 + -21 = 0
-21 + -4x + x2 = 0 + 4x + -4x
-21 + -4x + x2 = 4x + -4x

Combine like terms: 4x + -4x = 0
-21 + -4x + x2 = 0

Factor a trinomial.
(-3 + -1x)(7 + -1x) = 0

Subproblem 1Set the factor '(-3 + -1x)' equal to zero and attempt to solve:

Simplifying
-3 + -1x = 0

Solving
-3 + -1x = 0

Move all terms containing x to the left, all other terms to the right.

Add '3' to each side of the equation.
-3 + 3 + -1x = 0 + 3

Combine like terms: -3 + 3 = 0
0 + -1x = 0 + 3
-1x = 0 + 3

Combine like terms: 0 + 3 = 3
-1x = 3

Divide each side by '-1'.
x = -3

Simplifying
x = -3
Subproblem 2Set the factor '(7 + -1x)' equal to zero and attempt to solve:

Simplifying
7 + -1x = 0

Solving
7 + -1x = 0

Move all terms containing x to the left, all other terms to the right.

Add '-7' to each side of the equation.
7 + -7 + -1x = 0 + -7

Combine like terms: 7 + -7 = 0
0 + -1x = 0 + -7
-1x = 0 + -7

Combine like terms: 0 + -7 = -7
-1x = -7

Divide each side by '-1'.
x = 7

Simplifying
x = 7Solutionx = {-3, 7}

Answer 2

x =[ --4 +- sqrt(16 - 4x1x-21)] / 2
=( 4 + 10) / 2 = 7
also (4-10) / 2 = -3

solution set is {-3,7}

Answer 3

Did somebody just copy and paste bagatrix?

Answer 4

Actually its http://www.algebrahelp.com/

Answer 5

Same thing