4. A bundle of many sheets of paper in shape
of a rectangle makes up a cuboid.
We have used six rectangular pieces to
cover the complete outer surface of the
cuboid.
THEREFORE……..
Area of 4 rectangles = 2(lxb) + 2(bxh)
Curved Surface area = 2h(b+l)
Area of 6 rectangles = 2(lxb) + 2(bxh) + 2(lxh)
Total Surface area of a cuboid = 2 (lb + bh + hl)
CUBOIDS
5. Volume = Area of rectangle x height
= LB x H
=LBH
CUBOIDS
9. A cuboid, whose length, breadth and
height are all equal, it is called a Cube. If
each edge of the cube is a, then the
surface area of this cube would be:
Curved Surface Area of cube = 4a²
Total Surface area of a cube =6a²
CUBES
12. Take a number of
circular sheets of paper
and stack them up, if the
stack is kept vertically
up, we get a Right
circular cylinder, since it
has been kept at right
angles to the base, and
the base is circular.
CYLINDERS
13. So,
curved surface of the cylinder
= perimeter of the base of the
cylinder x h
= 2 ‫ח‬r x h
Therefore……….
Curved surface area of a cylinder = 2‫ח‬rh.
CYLINDERS