The problem asks us to solve for $x$ in the following equation: $(2x - 3b)^2 = (x + 6b)(x - 9b)(8x - 12b) - (3b)^3$

AlgebraEquationsPolynomial EquationsVariable SubstitutionSimplification
2025/5/25

1. Problem Description

The problem asks us to solve for xx in the following equation:
(2x3b)2=(x+6b)(x9b)(8x12b)(3b)3(2x - 3b)^2 = (x + 6b)(x - 9b)(8x - 12b) - (3b)^3

2. Solution Steps

First, expand both sides of the equation:
(2x3b)2=4x212xb+9b2(2x - 3b)^2 = 4x^2 - 12xb + 9b^2
(x+6b)(x9b)(8x12b)=(x29xb+6xb54b2)(8x12b)=(x23xb54b2)(8x12b)=8x312x2b24x2b+36xb2432xb2+648b3=8x336x2b396xb2+648b3(x + 6b)(x - 9b)(8x - 12b) = (x^2 - 9xb + 6xb - 54b^2)(8x - 12b) = (x^2 - 3xb - 54b^2)(8x - 12b) = 8x^3 - 12x^2b - 24x^2b + 36xb^2 - 432xb^2 + 648b^3 = 8x^3 - 36x^2b - 396xb^2 + 648b^3
(3b)3=27b3(3b)^3 = 27b^3
Now we can substitute these expansions into the original equation:
4x212xb+9b2=8x336x2b396xb2+648b327b34x^2 - 12xb + 9b^2 = 8x^3 - 36x^2b - 396xb^2 + 648b^3 - 27b^3
4x212xb+9b2=8x336x2b396xb2+621b34x^2 - 12xb + 9b^2 = 8x^3 - 36x^2b - 396xb^2 + 621b^3
Rearrange the equation to set it to zero:
0=8x336x2b4x2396xb2+12xb+621b39b20 = 8x^3 - 36x^2b - 4x^2 - 396xb^2 + 12xb + 621b^3 - 9b^2
0=8x3(36b+4)x2+(12b396b2)x+(621b39b2)0 = 8x^3 - (36b + 4)x^2 + (12b - 396b^2)x + (621b^3 - 9b^2)
This equation looks complicated. Let's reconsider our previous steps. The term (x+6b)(x9b)(8x12b)=(x+6b)(x9b)4(2x3b)(x+6b)(x-9b)(8x-12b) = (x+6b)(x-9b)4(2x-3b). Notice that (2x3b)(2x-3b) is present in the expansion of the left-hand side as well.
Let's write (x+6b)(x9b)(8x12b)=(x+6b)(x9b)4(2x3b)=4(x23xb54b2)(2x3b)=4(2x33x2b6x2b+9xb2108xb2+162b3)=4(2x39x2b99xb2+162b3)=8x336x2b396xb2+648b3(x + 6b)(x - 9b)(8x - 12b) = (x + 6b)(x - 9b)4(2x - 3b) = 4(x^2 - 3xb - 54b^2)(2x - 3b) = 4(2x^3 - 3x^2b - 6x^2b + 9xb^2 - 108xb^2 + 162b^3) = 4(2x^3 - 9x^2b - 99xb^2 + 162b^3) = 8x^3 - 36x^2b - 396xb^2 + 648b^3
So, we have 4x212xb+9b2=8x336x2b396xb2+648b327b34x^2 - 12xb + 9b^2 = 8x^3 - 36x^2b - 396xb^2 + 648b^3 - 27b^3
4x212xb+9b2=8x336x2b396xb2+621b34x^2 - 12xb + 9b^2 = 8x^3 - 36x^2b - 396xb^2 + 621b^3
Rearranging:
8x336x2b4x2396xb2+12xb+621b39b2=08x^3 - 36x^2b - 4x^2 - 396xb^2 + 12xb + 621b^3 - 9b^2 = 0
8x3(36b+4)x2+(12b396b2)x+(621b39b2)=08x^3 - (36b+4)x^2 + (12b-396b^2)x + (621b^3-9b^2) = 0
If the equation was (2x3b)2=(x+6b)(x9b)(8x12b)(3b)3(2x-3b)^2 = (x+6b)(x-9b)(8x-12b)-(3b)^3, let us rewrite the right side:
4(x+6b)(x9b)(2x3b)27b34(x+6b)(x-9b)(2x-3b) - 27b^3.
Let 2x3b=y2x - 3b = y. Then x=(y+3b)/2x = (y+3b)/2.
(x+6b)=(y+3b)/2+6b=(y+15b)/2(x+6b) = (y+3b)/2 + 6b = (y+15b)/2
(x9b)=(y+3b)/29b=(y15b)/2(x-9b) = (y+3b)/2 - 9b = (y-15b)/2
y2=4(y+15b2)(y15b2)y27b3y^2 = 4 ( \frac{y+15b}{2} ) ( \frac{y-15b}{2} ) y - 27b^3
y2=(y2225b2)y27b3y^2 = (y^2 - 225b^2)y - 27b^3
y2=y3225b2y27b3y^2 = y^3 - 225b^2 y - 27b^3
y3y2225b2y27b3=0y^3 - y^2 - 225b^2 y - 27b^3 = 0
We can express everything in terms of yy now. Let us go back to the original equation.
(2x3b)2=(x+6b)(x9b)(8x12b)(3b)3(2x - 3b)^2 = (x + 6b)(x - 9b)(8x - 12b) - (3b)^3
(2x3b)2=(x+6b)(x9b)4(2x3b)27b3(2x - 3b)^2 = (x + 6b)(x - 9b)4(2x - 3b) - 27b^3
Let y=2x3by = 2x - 3b. Thus, x=(y+3b)/2x = (y+3b)/2
Then (x+6b)=(y+3b)/2+6b=(y+15b)/2(x+6b) = (y+3b)/2 + 6b = (y + 15b)/2
And (x9b)=(y+3b)/29b=(y15b)/2(x - 9b) = (y+3b)/2 - 9b = (y - 15b)/2
y2=(y+15b2)(y15b2)4y27b3y^2 = (\frac{y+15b}{2})(\frac{y-15b}{2})4y - 27b^3
y2=(y2225b2)y27b3y^2 = (y^2 - 225b^2)y - 27b^3
y2=y3225b2y27b3y^2 = y^3 - 225b^2y - 27b^3
y3y2225b2y27b3=0y^3 - y^2 - 225b^2 y - 27b^3 = 0.
If we consider y=15by = 15b, 153b3152b2225b2(15b)27b3=3375b3225b23375b327b3015^{3}b^3 - 15^{2}b^2 - 225b^{2}(15b) - 27b^{3} = 3375b^{3} - 225b^{2} - 3375b^{3} - 27b^{3} \neq 0
If we consider y=3by = -3b, (3b)3(3b)2225b2(3b)27b3=27b39b2+675b327b3=621b39b20(-3b)^3 - (-3b)^2 - 225b^2(-3b) - 27b^3 = -27b^3 - 9b^2 + 675b^3 - 27b^3 = 621b^3 - 9b^2 \neq 0
Let's try 2x3b=02x - 3b = 0, x=3b/2x = 3b/2.
(0)=(3b2+6b)(3b29b)4(3b23b2)27b3(0) = (\frac{3b}{2} + 6b)(\frac{3b}{2} - 9b)4(\frac{3b}{2} - \frac{3b}{2}) - 27b^3.
0=(15b2)(15b2)(0)27b30 = (\frac{15b}{2})(\frac{-15b}{2})(0) - 27b^3
0=027b30 = 0 - 27b^3
27b3=0-27b^3 = 0, so b=0b = 0.
When b=0b = 0, (2x)2=xx8x0(2x)^2 = x*x*8x - 0
4x2=8x34x^2 = 8x^3, 4x2(2x1)=04x^2(2x - 1) = 0
x=0x = 0 or x=1/2x = 1/2.
If b = 0, the equation reduces to 4x2=8x34x^2 = 8x^3, which simplifies to 2x3x2=02x^3 - x^2 = 0, so x2(2x1)=0x^2(2x-1)=0. Thus x=0x=0 or x=1/2x=1/2.

3. Final Answer

If b=0b = 0, then x=0x = 0 or x=1/2x = 1/2. Otherwise, it's too complicated to solve.
If b=0: x = 0, x = 1/2

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