Saturday, August 22, 2015

Find the sides of a rectangular prism if the volume = 30 cm^3 , the height = 3 cm and the perimeter of the base = 14 cm.

Volume of a rectangular prism is given by the
formula:


Volume = (Area of the rectangular cross
section)*Height


substituting given values of height and
volume in the above formula:


30 = (Area of the rectangular
cross
section)*3


Therefore:


Area of
the rectangular cross section = 30/3 = 10 cm^2


Let lengths
of two side of the triangle be x and
y


Then:


Area of rectangle =
x*y = 10


Therefore:


y =
10/x


And:


Perimeter of the
rectangle = 2*(x + y) = 14


==> x + y =
7


Substituting values of y as 10/x in above
equation:


x + 10/x =
7


Multiplying both sides by x, and shifting all the terms
of equation on left hand side:


x^2 - 7x + 10 =
0


==> x^2 - 2x - 5x + 10 =
0


==> x(x - 2) - 5(x - 2) =
0


==> (x - 2)(x - 5) =
0


Therefore:


x = 2 or
5


Therefore sides of the rectangular prism are 2 cm and 5
cm.

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