Calculate C¹B¹ in a Rectangular Prism with Diagonal √(6x²-12x+41)

Question

ABCDA1B1C1D1 ABCDA^1B^1C^1D^1 is a rectangular prism.

The length of its diagonal is

6x212x+41 \sqrt{6x^2-12x+41} .


DC1=5x24x+25 DC^1=\sqrt{5x^2-4x+25}

Calculate C1B1 C^1B^1 .

AAABBBCCCDDDAAA111BBB111CCC111DDD111

Video Solution

Solution Steps

00:16 First, let's calculate C one B one.
00:25 Each face of the box is a rectangle, so every angle is a right angle.
00:34 Now, use the Pythagorean theorem in triangle D B one C one to find C one B one.
00:45 Substitute the given values and solve for C one B one.
01:06 Next, isolate C one B one and simplify the terms.
01:23 And that's how we solve this problem.

Step-by-Step Solution

To solve this problem, we'll use the expressions for the diagonals given:

  • The space diagonal of the prism: 6x212x+41 \sqrt{6x^2 - 12x + 41} .
  • The face diagonal DC1=5x24x+25 DC^1 = \sqrt{5x^2 - 4x + 25} .
  • We need to find the edge C1B1 C^1B^1 .

Since DC1=a2+b2 DC^1 = \sqrt{a^2 + b^2} , we will denote one dimension as aa and another as bb. Therefore:

DC1=5x24x+25=(x2)2+(b)2 DC^1 = \sqrt{5x^2 - 4x + 25} = \sqrt{(x-2)^2 + (b)^2} .

Assuming that x2x-2 is one of the lengths, we have:

5x24x+25=(x2)2+b2 5x^2 - 4x + 25 = (x-2)^2 + b^2 .

On expanding (x2)2(x-2)^2, we get x24x+4 x^2 - 4x + 4 . Thus:

5x24x+25=x24x+4+b2 5x^2 - 4x + 25 = x^2 - 4x + 4 + b^2 .

Cancelling the x24xx^2 - 4x terms on both sides gives,

4x2+21=b2 4x^2 + 21 = b^2 .

For the diagonal of the prism, we assume if x2 x-2 is one dimension and b=4x2+21 b = \sqrt{4x^2 + 21} , we solve:

(6x212x+41)2=(x2)2+(b)2+(C1B1)2 \left(\sqrt{6x^2 - 12x + 41}\right)^2 = (x-2)^2 + (b)^2 + ( C^1B^1 )^2 .

6x212x+41=(x2)2+4x2+21+(C1B1)2 6x^2 - 12x + 41 = (x-2)^2 + 4x^2 + 21 + (C^1B^1)^2 .

Substituting (x2)2=x24x+4 ( x-2 )^2 = x^2 - 4x + 4 :

6x212x+41=x24x+4+4x2+21+(C1B1)2 6x^2 - 12x + 41 = x^2 - 4x + 4 + 4x^2 + 21 + (C^1B^1)^2 .

Simplify and solve for C1B1 C^1B^1 :

6x212x+41=5x2+25+(C1B1)2 6x^2 - 12x + 41 = 5x^2 + 25 + (C^1B^1)^2.

Thus, x212x+16=(C1B1)2x^2 - 12x + 16 = (C^1B^1)^2.

This implies C1B1=x4C^1B^1 = x - 4.

Therefore, the solution to the problem is C1B1=x4 C^1B^1 = x-4 .

Answer

x4 x-4