Math Is Fun Forum

Heldensheld

Member

Registered: 2006-07-01

Posts: 25

Help~ Don't know how to do these...please show me how...

Right...so I have a test tomorrow that might have questions like these in it....could some of youse help me with two questions and show me how youse came to this conclusion?

Q1.  A rectangular swimming pool is 12m long by 6m wide. It is surroudned by a pavement of uniform width, the area of the pavement being 7/8 of the area of the pool.

a) If the pavement is Xm wide, show that the area of the pavement is 4x^2 + 36x m^2.
b) Hence, show that 4x^2 +36x -63 = 0
c) How wide is the pavement?

Q2.  A circular magnet has an inner radius x cm and an outer radius 2cm larger and its depth is the same as the inner radius. If the total volume of the magnet is 120pii cm^3. Find X.

Danke!

George,Y

Member

Registered: 2006-03-12

Posts: 1,379

Re: Help~ Don't know how to do these...please show me how...

Simple solution:
The pavement and the pool altogether form a larger rectangular, (12+2x)m by (6+2x)m.
So the area of the pavement is:
(12+2x) (6+2x) - 12 6 = 24x+12x+4x²= 36x+4x² (m²)
To solve the x, use the identity of the pool area:
36x+4x² (m²)=7/8 12 6

The answer to Q2:
120 Pi = x Pi((x+2)²-x²)
You can solve Pi now

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X'(y-Xβ)=0

Heldensheld

Member

Registered: 2006-07-01

Posts: 25

Re: Help~ Don't know how to do these...please show me how...

Thanks George.

George,Y

Member

Registered: 2006-03-12

Posts: 1,379

Re: Help~ Don't know how to do these...please show me how...

You are welcome

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X'(y-Xβ)=0