Questions   
Sort: 
 #2
avatar
+1
May 25, 2018
May 24, 2018
 #2
avatar+258 
0
May 24, 2018
 #3
avatar+12528 
+2
May 24, 2018
 #1
avatar
+3

Hi Max. Sorry, no LaTex!

2.         Solve for x:

x^2 + 7 x - 5 = 5 sqrt(x^3 - 1)

 

x^2 + 7 x - 5 = 5 sqrt(x^3 - 1) is equivalent to 5 sqrt(x^3 - 1) = x^2 + 7 x - 5:

5 sqrt(x^3 - 1) = x^2 + 7 x - 5

 

Raise both sides to the power of two:

25 (x^3 - 1) = (x^2 + 7 x - 5)^2

 

Expand out terms of the left hand side:

25 x^3 - 25 = (x^2 + 7 x - 5)^2

 

Expand out terms of the right hand side:

25 x^3 - 25 = x^4 + 14 x^3 + 39 x^2 - 70 x + 25

 

Subtract x^4 + 14 x^3 + 39 x^2 - 70 x + 25 from both sides:

-x^4 + 11 x^3 - 39 x^2 + 70 x - 50 = 0

 

The left hand side factors into a product with three terms:

-(x^2 - 8 x + 10) (x^2 - 3 x + 5) = 0

 

Multiply both sides by -1:

(x^2 - 8 x + 10) (x^2 - 3 x + 5) = 0

Split into two equations:

x^2 - 8 x + 10 = 0 or x^2 - 3 x + 5 = 0

 

Subtract 10 from both sides:

x^2 - 8 x = -10 or x^2 - 3 x + 5 = 0

 

Add 16 to both sides:

x^2 - 8 x + 16 = 6 or x^2 - 3 x + 5 = 0

 

Write the left hand side as a square:

(x - 4)^2 = 6 or x^2 - 3 x + 5 = 0

 

Take the square root of both sides:

x - 4 = sqrt(6) or x - 4 = -sqrt(6) or x^2 - 3 x + 5 = 0

 

Add 4 to both sides:

x = 4 + sqrt(6) or x - 4 = -sqrt(6) or x^2 - 3 x + 5 = 0

 

Add 4 to both sides:

x = 4 + sqrt(6) or x = 4 - sqrt(6) or x^2 - 3 x + 5 = 0

Subtract 5 from both sides:

x = 4 + sqrt(6) or x = 4 - sqrt(6) or x^2 - 3 x = -5

 

Add 9/4 to both sides:

x = 4 + sqrt(6) or x = 4 - sqrt(6) or x^2 - 3 x + 9/4 = -11/4

 

Write the left hand side as a square:

x = 4 + sqrt(6) or x = 4 - sqrt(6) or (x - 3/2)^2 = -11/4

 

Take the square root of both sides:

x = 4 + sqrt(6) or x = 4 - sqrt(6) or x - 3/2 = (i sqrt(11))/2 or x - 3/2 = 1/2 (-i) sqrt(11)

 

Add 3/2 to both sides:

x = 4 + sqrt(6) or x = 4 - sqrt(6) or x = 3/2 + (i sqrt(11))/2 or x - 3/2 = -(i sqrt(11))/2

 

Add 3/2 to both sides:

 

x = 4 + sqrt(6) or x = 4 - sqrt(6) or x = 3/2 + (i sqrt(11))/2 or x = 3/2 - (i sqrt(11))/2

[4 + sqrt(6)] * [4 - sqrt(6)]= 10

[Courtesy of Mathematica 11 Home Edition]

May 24, 2018

6 Online Users

avatar
avatar
avatar
avatar