This Post Has 3 Comments

1. starting with:    

   5 + x - 12 = 2x - 7   

   5 + x - 12 - x = 2x - 7 - x (subtract x from both sides)   

   5 - 12 = x - 7 (combine and cancel x's from both sides)   

   5 - 12 + 7 = x - 7 + 7 (add 7 to both sides)   

   0 = x (add numbers together on both sides)       

   so in order for the equation to be true, x must be 0.   

   trying x = -0.5   

   5 + x - 12 = 2x - 7 (original equation)   

   5 + -0.5 - 12 = 2(-0.5) - 7 (plug in value of x)   

   5 + -0.5 - 12 = -1 - 7 (did multiplication)   

   -7.5 = -8 (did addition on both sides)       

   since -7.5 is obviously not equal to -8, the value of -0.5 for x is wrong.   

   trying x = 0   

   5 + x - 12 = 2x - 7 (original equation)   

   5 + 0 - 12 = 2(0) - 7 (plug in value of x)   

   5 + 0 - 12 = 0 - 7 (did multiplication)   

   -7 = -7 (did addition on both sides)       

   since -7 equals -7, that demonstrates that the value of 0 for x is correct.   

   trying x = 1   

   5 + x - 12 = 2x - 7 (original equation)   

   5 + 1 - 12 = 2(1) - 7 (plug in value of x)   

   5 + 1 - 12 = 2 - 7 (did multiplication)   

   -6 = -5 (did addition on both sides)       

   since -6 is obviously not equal to -5, the value of 1 for x is wrong.

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2. Surface area of the reflective glass is 543234.4 square feet.

   Step-by-step explanation:

   Given that: height = 311 feet, sides of square base = 619 feet.

   To determine the slant height, we have;

   [tex]l^{2}[/tex] = [tex]311^{2}[/tex] + [tex]309.5^{2}[/tex]

      = 96721 + 95790.25

      = 192511.25

   ⇒ l = [tex]\sqrt{192511.25}[/tex]

         = 438.761

   The slant height, l is 438.8 feet.

   Considering one reflecting surface of the pyramid, its area = [tex]\frac{1}{2}[/tex] × base × height

     area =  [tex]\frac{1}{2}[/tex] × 619 × 438.8

             = 135808.6

             = 135808.6 square feet

   Since the pyramid has four reflective surfaces,

   surface area of the reflective glass = 4 × 135808.6

                                                             = 543234.4 square feet

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3. just sum

   10 + 10 = 20

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