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Integral Calculus. A mathematical description of motion motivated the creation of Calculus. Problem of Motion: Given x ( t ) find v ( t ) : Differential Calculus. Given v ( t ) find x ( t ) : Integral Calculus. Derivatives and integrals are operations on functions.
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Integral Calculus A mathematical description of motion motivated the creation of Calculus. Problem of Motion: Given x(t) find v(t) : Differential Calculus. Given v(t) find x(t) : Integral Calculus. Derivatives and integrals are operations on functions. One is the inverse of the other. This is the content of the Fundamental theorem of Calculus.
Integral calculus is mainly due to the contributions from the following well known mathematicians.(The photographs are worth watching since these names will appear many times in the courses to follow.) Isaac Newton Gottfried Leibniz
James Gregory Pierre de Fermat
Joseph Fourier Cauchy
Bernhard Riemann Henri Lebesgue
Some motivations:1. Suspension bridges The road deck hangs on vertical cables suspended from the main cables. Problem : We have to find the optimal shape of the main cable.
Mathematical description (Model): Solution: This is the basic problem of integral calculus and we solve the problem by integration. y(x) = y′(x) dx = μx dx = μ (x2/2) + C. The main cable has a parabolic shape.
REDUCTION FORMULAE Reduction formula for sinn x dx where n is a positive integer. Let In = sinnx dx = sinn-1 x.sin x. dx = u v dx (say) We know that uv dx = u ( v dx) - ( v dx ) u1 dx In = sinn-1 x (-cos x) - (-cos x) (n – 1) sinn-2 x. cos x dx = - sinn-1 x cos x + ( n – 1) sinn-2 x.cos2 x dx = - sinn-1 x cos x + (n – 1) sinn-2 x (1 – sin2 x) dx = - sinn-1 x cos x + (n – 1) sinn-2 x dx – (n – 1) In
In [1 + (n – 1)] = - sinn-1 x cos x + ( n – 1) In-2 Therefore In = sinn x dx = • is the required reduction formula. • Illustration (i): To find sin4 x dx.
I4 = sin4 x dx = We need to apply the result (1) again by taking n = 2 That is, I4 = I0 = sin0 x dx = 1 dx = x Thus I4 = sin4 x dx =
Illustration (ii): To find sin5 x dx Solution: I5 = sin5 x dx = But I1 = sin1 x dx = - cos x.
Corollary : To evaluate From (1) , In = But cos /2 = 0 = sin 0. Thus In =
Now, In-2 = In = Continuing the process we get: I1 if n is odd. In = I0 if n is even. But I1 = - [cos x]0/2 = - (0 – 1) = 1 and I0 =
.1 if n is odd. = if n is even.
Evaluation of Integrals: where n is a positive integer. • We put x = sin • Note that when x = 0, = 0 and when x = 1, = /2. • we get
We put x = tan Note that when x = 0, = 0 and when x , /2
Reduction formula for Im,n = sinm x cosn x dx: Write Im,n = (sinm-1 x) (sin x cosn x)dx Then Im,n = - (m – 1) sinm-2 x cos x sinm-2 x cosn x (1 – sin2 x) dx
Evaluation of Thus we get
Changing m to m – 2 successively, we have …… Finally I3,n = if m is odd I2,n = if m even
Case (i): When m is odd (and n is even or odd), Case (ii): When m is even and n is odd, Case (iii): When m and n are both even,
Evaluation of Integrals : Put x = tan , Sol: These values can be computed.
Put x = a sin2 Then dx = 2a sin cos d ; varies from 0 to /2. = a sin cos .
Example : If n is a positive integer, show that Solution: First we note that Now we put a – x = a cos . Then x = a (1 – cos ) = 2a sin2 (/2); when x = 0, = 0 and when x = 2a, = .
Reduction formula for In = tann x dx: In = (tann-2 x) (tan2 x) dx = (tann-2 x) (sec2 x – 1) dx = tan n-2 x sec2 x dx - tann-2 x dx This is the reduction formula .
On changing n to n – 2 successively, The last expression is I1 if n is odd and I0 if n is even .
= [ log sec x]0/4 = - … …..I where I = I1 if n is odd, I = I0 if n is even andI appears with appropriate sign