Respuesta :
The error is: He used an expression for surface area that did not include all the faces.
What is a rectangular pyramid?
"It is a pyramid having a rectangular base."
What is surface area?
"The surface area of a geometrical structure is the sum of all its surfaces."
For given example,
He derived an expression to find the surface area of the rectangular prism is : (4.2) (9.6) + one-half (4.2) (6.5) + one-half (9.6) (4.8)
The rectangular base has a length of 9.6 millimeters and width of 4.2 millimeters.
So, the surface area of the base would be,
(9.6) × (4.2) ................................(1)
2 triangular sides have a base of 9.6 millimeters and height of 4.8 millimeters.
The area of the one triangular side with a base of 9.6 millimeters and height of 4.8 millimeters would be,
1/2 × 9.6 × 4.8
So, the area of two triangular sides would be,
(1/2 × 9.6 × 4.8) + (1/2 × 9.6 × 4.8) .....................(2)
2 triangular sides have a base of 4.2 millimeters and height of 6.5 millimeters.
The area of the one triangular side with a base of 4.2 millimeters and height of 6.5 millimeters would be,
1/2 × 4.2 × 6.5
So, the area of two triangular sides would be,
(1/2 × 4.2 × 6.5) + (1/2 × 4.2 × 6.5) .....................(3)
From (1), (2) and (3),
The expression to find the total surface area of rectangular prism should be,
(9.6) × (4.2) + (1/2 × 9.6 × 4.8) + (1/2 × 9.6 × 4.8) + (1/2 × 4.2 × 6.5) + (1/2 × 4.2 × 6.5)
This means, he used an expression for surface area that did not include all the faces.
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