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Division by Zero
Everyone knows that0/2=0 , the problem is that far too many people also say that
or 2 = 2 ! Remember that division by zero is undefined! You simply cannot divide by
0
zero so don’t do it!
Here is a very good example of the kinds of havoc that can arise when you divide by zero. See if you can find the mistake that I made in the work below.
1. a = b We’ll start assuming this to be true.
2. ab = a ^2 Multiply both sides by a.
3. ab - b^2 = a^ 2 - b^2 Subtract b^2 from both sides.
4. b ( a - b) = ( a + b ) ( a - b )Factor both sides.
5. b = a + b Divide both sides by a - b .
6. b = 2b Recall we started off assuming a = b .
7. 1 = 2 Divide both sides by b.
So, we’ve managed to prove that 1 = 2! Now, we know that’s not true so clearly we
made a mistake somewhere. Can you see where the mistake was made?
The mistake was in step 5. Recall that we started out with the assumption a = b .
However, if this is true then we have a - b = 0 ! So, in step 5 we are really dividing by zero!
That simple mistake led us to something that we knew wasn’t true, however, in most
cases your answer will not obviously be wrong. It will not always be clear that you are dividing by zero, as was the case in this example. You need to be on the lookout for this kind of thing.
Remember that you CAN’T divide by zero!
An increasing function is a function where: if x1 > x2, then f(x1) > f(x2) , so as x increases, f(x) increases. A decreasing function is a function which decreases as x increases. Of course, a function may be increasing in some places and decreasing in others. A point where a function changes from an increasing to a decreasing function or visa-versa is known as a turning point. A turning point is a type of stationary point (see below).
We can use differentiation to determine if a function is increasing or decreasing:
A function is increasing if its derivative is always positive. A function is decreasing if its derivative is always negative.
y = -x has derivative -1 which is always negative and so -x is decreasing.
y = x2 has derivative 2x, which is negative when x is less than zero and positive when x is greater than zero. Hence x2 is decreasing for x<0>0 .
Stationary points are points on a graph where the gradient is zero. There are three types of stationary points: maximums, minimums and points of inflection (/inflexion). The three are illustrated here:
Find the coordinates of the stationary points on the graph y = x2 .
We know that at stationary points, dy/dx = 0 (since the gradient is zero at stationary points).
By differentiating, we get: dy/dx = 2x. Therefore the stationary points on this graph occur when 2x = 0, which is when x = 0.
When x = 0, y = 0, therefore the coordinates of the stationary point are (0,0). In this case, this is the only stationary point. If you think about the graph of y = x2, you should know that it is "U" shaped, with its lowest point at the origin. This is what we have just found.
At all the stationary points, the gradient is the same (= zero) but it is often necessary to know whether you have found a maximum point, a minimum point or a point of inflection. Therefore the gradient at either side of the stationary point needs to be looked at (alternatively, we can use the second derivative).
At maximum points, the gradient is positive just before the maximum, it is zero at the maximum and it is negative just after the maximum. At minimum points, the gradient is negative, zero then positive. Finally at points of inflexion, the gradient can be positive, zero, positive or negative, zero, negative. This is illustrated here:
Find the stationary points on the graph of y = 2x2 + 4x3 and state their nature (i.e. whether they are maxima, minima or points of inflexion).
dy/dx = 4x + 12x2
At stationary points, dy/dx = 0
Therefore 4x + 12x2 = 0 at stationary points
Therefore 4x( 1 + 3x ) = 0
Therefore either 4x = 0 or 3x = -1
Therefore x = 0 or -1/3
When x = 0, y = 0
When x = -1/3, y = 2x2 + 4x3 = 2(-1/3)2 + 4(-1/3)3 = 2/9 - 4/27 = 2/27
Looking at the gradient either side of x = 0:
When x = -0.0001, dy/dx = negative
When x = 0, dy/dx = zero
When x = 0.0001, dy/dx = positive
So the gradient goes -ve, zero, +ve, which shows a minimum point.
Looking at the gradient either side of x = -1/3 .
When x = -0.3334, dy/dx = +ve
When x = -0.3333..., dy/dx = zero
When x = -0.3332, dy/dx = -ve
So the gradient goes +ve, zero, -ve, which shows a maximum point.
Therefore there is a maximum point at (-1/3 , 2/27) and a minimum point at (0,0).
This method of finding maxima and minima is very useful and can be used to find the maximum and minimum values of all sorts of things.
Find the least area of metal required to make a closed cylindrical container from thin sheet metal in order that it might have a capacity of 2000p cm3.
The total surface area of the cylinder, S, is 2pr2 + 2prh
The volume = pr2h = 2000p
Therefore pr2h = 2000p.
Therefore h = 2000/r2
Therefore S = 2pr2 + 2pr( 2000/r2 )
= 2pr2 + 4000p
r
So we have an expression for the surface area. To find when the surface area is a minimum, we need to find dS/dr .
dS = 4pr - 4000p
dr r2
When dS/dr = 0:
4pr - (4000p)/r2 = 0
Therefore 4pr = 4000p
r2
So 4pr3 = 4000p
So r3 = 1000
So r = 10
You should then check that this is indeed a minimum using the technique above.
So the minimum area occurs when r = 10. This minimum area is found by substituting into the equation for the area the value of r = 10.
S = 2pr2 + 4000p
r
= 2p(10)2 + 4000p
10
= 200p + 400p
= 600p
Therefore the minimum amount of metal required is 600p cm2
STORY OF PI
Did u know that Archimedes was the first mathematician to discover the value of pi up to 10000 digits!!!
Who was the first mathematician to give the approximate value of “pi” which is commonly accepted today? YES IT IS INDIAN Aryabhata(he gave the value of pi as 3.1416)
Notes on Pi: Pi is the most famous ratio in mathematics, and is one of the most ancient numbers known to humanity. Pi is approximately 3.14 – the number of times that a circle’s diameter will fit around the circle. Pi goes on forever, and can’t be calculated to perfect precision: 3.1415926535897932384626433832795028841971693993751…. This is known as the decimal expansion of pi. No apparent pattern emerges in the succession of digits – a predestined yet unfathomable code. They do not repeat periodically, seemingly to pop up by blind chance, lacking any perceivable order, rule, reason, or design – “random” integers, ad infinitum.
In 1991, the Chudnovsky brothers in
Pi has had various names through the ages, and all of them are either words or abstract symbols, since pi is a number that can’t be shown completely and exactly in any finite form of representation. Pi is a transcendental number. A transcendental number is a number but can’t be expressed in any finite series of either arithmetical or algebraic operations. Pi slips away from all rational methods to locate it. It is indescribable and can’t be found. Ferdinand Lindemann, a German mathematician, proved the transcendence of pi in 1882.
Pi possibly first entered human consciousness in
Around 200 BCE, Archimedes of Syracuse found that pi is somewhere about 3.14 (in fractions, Greeks did not have decimals). Knowledge of pi then bogged down until the 17th century. Pi was then called the Ludolphian number, after Ludolph van Ceulen, a German mathematician. The first person to use the Greek letter for the number was William Jones, an English mathematician, who coined it in 1706.
Physicists have noted the ubiquity of pi in nature. Pi is obvious in the disks of the moon and the sun. The double helix of DNA revolves around pi. Pi hides in the rainbow, and sits in the pupil of the eye, and when a raindrop falls into water pi emerges in the spreading rings. Pi can be found in waves and ripples and spectra of all kinds, and therefore pi occurs in colours and music. Pi has lately turned up in superstrings.
Pi occurs naturally in tables of death, in what is known as a Gaussian distribution of deaths in a population; that is, when a person dies, the event “feels” pi. It is one of the great mysteries why nature seems to know mathematics.
(NOTE: The above information was gleaned from an article in The New Yorker magazine, March 2, 1992, called “Profiles: The Mountains of Pi”)