Q. When a body has uniform cross-section, its surface area (excluding cross-section) = Perimeter of cross -section x length.. Explain the above lines/

2. the surface area excluding the cross section surface area is known as cured surface area.let understand this with example take a cylinder of height h and radius rso the curved surface area=perimeter of the cross section that is perimeter of the circle of radius r*length that is height h=2πrh   that we know the CSA of the cylinder .so this true for any unform cross section shape .Regards

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Let us take a cylinder
cross-section is a circle
area of cross-section is area of circle with radius r
which is (22/7)*r2
Volume is "area of cross-section"*height  let h be the height
=(22/7)*r2 *h

SA of excluding cross-section is SA of the curved part of the cylinder
Perimeter of cross section which is perimeter of circle which is circumference of the circle i.e. 2(22/7)*r # r being the radius
SA of cylinder curved part is Circumference of cylinder * length
= SA (excluding cross-section)
= Perimeter of cross section * length
= 2*(22/7)*r*h

This analogy can be applied to any UNIFORM surface i.e. cuboid
perimeter of cross section = 2(l+b)
height = h
SA (excluding cross-section)
=perimeter of cross section * height
=2(l+b)*h # Areas of cuboid excluding the roof and floor
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