12th Grade > Mathematics
DEFINITE INTEGRATION MCQs
Total Questions : 30
| Page 3 of 3 pages
Answer: Option B. -> x3ex
:
B
f(x)=∫xat3etdt=∫0at3.etdt+∫x0t3etdt
⇒df(x)dx=ddx(∫0at3.etdt)+ddx(∫x0t3.etdt)=x3ex
:
B
f(x)=∫xat3etdt=∫0at3.etdt+∫x0t3etdt
⇒df(x)dx=ddx(∫0at3.etdt)+ddx(∫x0t3.etdt)=x3ex
Answer: Option D. -> I=I4
:
D
For 0 < x < 1, we have 12x2<x2<x
⇒−x2>−x,sothate−x2<e−x,
Hence∫10e−x2cos2xdx>∫10e−xcos2xdx
Alsocos2x≤1
Therefore∫10e−x2cos2xdx≤∫10e−x2dx<∫10e−x22dx=I4
Hence I4 is the greatest integral
:
D
For 0 < x < 1, we have 12x2<x2<x
⇒−x2>−x,sothate−x2<e−x,
Hence∫10e−x2cos2xdx>∫10e−xcos2xdx
Alsocos2x≤1
Therefore∫10e−x2cos2xdx≤∫10e−x2dx<∫10e−x22dx=I4
Hence I4 is the greatest integral
Answer: Option D. -> loge 2
:
D
limn→∞[1n+1n+1+1n+2+⋯+12n]
=limn→∞[1n+1n+1+1n+2+⋯+1n+n]
=1nlimn→∞[1+11+1n+11+2n+⋯+11+nn]
=1nlimn→∞∑nr=0[11+rn]=∫1011+xdx
=[loge(1+x)]10=loge2−loge1=loge2
:
D
limn→∞[1n+1n+1+1n+2+⋯+12n]
=limn→∞[1n+1n+1+1n+2+⋯+1n+n]
=1nlimn→∞[1+11+1n+11+2n+⋯+11+nn]
=1nlimn→∞∑nr=0[11+rn]=∫1011+xdx
=[loge(1+x)]10=loge2−loge1=loge2
Answer: Option B. -> 13
:
B
I=∫10x7√1−x4dx=∫10x6xdx√1−x4
Putx2=sinθ⇒2xdx=cosθdθ
I=12π20sin3θ.cosθdθcosθ=12∫120sin3θdθ
=12T2T(12)2.T(12)=T(12)4.32.12.T(12)=13
:
B
I=∫10x7√1−x4dx=∫10x6xdx√1−x4
Putx2=sinθ⇒2xdx=cosθdθ
I=12π20sin3θ.cosθdθcosθ=12∫120sin3θdθ
=12T2T(12)2.T(12)=T(12)4.32.12.T(12)=13
Answer: Option D. -> 3π8
:
D
∫π0|sin4x|dx=2∫π20sin4xdx
Applying gamma function,
2∫π20sin4xdx=2T(52).T(12)2.T(62)=3π8
:
D
∫π0|sin4x|dx=2∫π20sin4xdx
Applying gamma function,
2∫π20sin4xdx=2T(52).T(12)2.T(62)=3π8
Answer: Option C. -> 15
:
C
We have seen that if g(y)≥0 for yϵ [c, d] then the area bounded by curve x = g(y) and y-axis between abscissa y = c and y = d is ∫d(y=c)g(y)dy .
We'll use the same concept here. Here the curve given is
x=y2+2 and c = 0 &d=3.So,g(y)≥0∀xϵ(0,3)
Let the area enclosed be A.
A=∫30(y2+2)dy.
A=(y33+2y)|30A=9+6−0A=15
:
C
We have seen that if g(y)≥0 for yϵ [c, d] then the area bounded by curve x = g(y) and y-axis between abscissa y = c and y = d is ∫d(y=c)g(y)dy .
We'll use the same concept here. Here the curve given is
x=y2+2 and c = 0 &d=3.So,g(y)≥0∀xϵ(0,3)
Let the area enclosed be A.
A=∫30(y2+2)dy.
A=(y33+2y)|30A=9+6−0A=15
Answer: Option A. -> 43
:
A
y2=xand2y=x⇒y2=2y⇒y=0,2
∴Requiredarea=∫20(y2−2y)dy=(y33−y2)20=43sq.unit
:
A
y2=xand2y=x⇒y2=2y⇒y=0,2
∴Requiredarea=∫20(y2−2y)dy=(y33−y2)20=43sq.unit
Answer: Option A. -> True
:
A
With all the information given let’s draw the graph of f(x) on cartesian coordinate system.
The area which we are interested in calculating is the area PRSQP. To calculate this area let’s divide this into rectangles of equal and infinitesimally small width. Now, what’s the purpose of this? Why are we doing this? Let’s discuss them one by one.
First why rectangle? Very simple, we do not know any approach to calculate the area of graphs like this. But we do know how to calculate the area of rectangle.
Second why infinitesimally small width? Just because we know how to calculate the area of rectangle we can’t calculate the area of this graph.
For example if we divide the stretch a to b in two parts, i.e. dividing it into two rectangles of equal width will give us area which is not equal to the area of this graph. The difference between the area of the rectangles and the area of this graph will be significant. So, to reduce this error of the difference we’ll divide this graph into infinite rectangles.
So, the the length a to b which is b−a will be divided into n equal parts giving width as b−an
Now consider regions ABCD, ABLC, ABDM.
By observation we can say -
Area of the rectangle ABLC < area of the region ABCD < Area of the rectangle ABDM
Actually when the width becomes infinitesimally small all these area become nearly equal to each other.
limn→∞b−an Area of the rectangle ABLC ≈ Area of the region ABCD ≈ Area of the rectangle ABDM
Now we form the sums -
sn=b−an[f(a)+f(a+h)...f(a+(n−1)h)]
Sn=b−an[f(a+h)+f(a+2h)...f(a+nh)]
Where, sn&Sn denote the sum of the areas of lower rectangles and upper rectangles respectively.
And we know, sn<AreaPRSQP<Sn
As n→∞ strips becomes narrower and narrower and both the sum becomes equal.
So, limn→∞sn = Area PRSQP = limn→∞Sn
b−an=h(given)
So, Area of the graph =
limn→∞b−an[f(a)+f(a+h)...f(a+(n−1)h)]
:
A
With all the information given let’s draw the graph of f(x) on cartesian coordinate system.
The area which we are interested in calculating is the area PRSQP. To calculate this area let’s divide this into rectangles of equal and infinitesimally small width. Now, what’s the purpose of this? Why are we doing this? Let’s discuss them one by one.
First why rectangle? Very simple, we do not know any approach to calculate the area of graphs like this. But we do know how to calculate the area of rectangle.
Second why infinitesimally small width? Just because we know how to calculate the area of rectangle we can’t calculate the area of this graph.
For example if we divide the stretch a to b in two parts, i.e. dividing it into two rectangles of equal width will give us area which is not equal to the area of this graph. The difference between the area of the rectangles and the area of this graph will be significant. So, to reduce this error of the difference we’ll divide this graph into infinite rectangles.
So, the the length a to b which is b−a will be divided into n equal parts giving width as b−an
Now consider regions ABCD, ABLC, ABDM.
By observation we can say -
Area of the rectangle ABLC < area of the region ABCD < Area of the rectangle ABDM
Actually when the width becomes infinitesimally small all these area become nearly equal to each other.
limn→∞b−an Area of the rectangle ABLC ≈ Area of the region ABCD ≈ Area of the rectangle ABDM
Now we form the sums -
sn=b−an[f(a)+f(a+h)...f(a+(n−1)h)]
Sn=b−an[f(a+h)+f(a+2h)...f(a+nh)]
Where, sn&Sn denote the sum of the areas of lower rectangles and upper rectangles respectively.
And we know, sn<AreaPRSQP<Sn
As n→∞ strips becomes narrower and narrower and both the sum becomes equal.
So, limn→∞sn = Area PRSQP = limn→∞Sn
b−an=h(given)
So, Area of the graph =
limn→∞b−an[f(a)+f(a+h)...f(a+(n−1)h)]
Answer: Option D. -> Hyperbola
:
D
In+1=∫π20cosn+1xcos(n+1)xdx=∫π20cosn+1x(cosnxcosx−sinnxsinx)dx∴In+1=In−In+1⇒2In+1=In∴In:In+1=2
:
D
In+1=∫π20cosn+1xcos(n+1)xdx=∫π20cosn+1x(cosnxcosx−sinnxsinx)dx∴In+1=In−In+1⇒2In+1=In∴In:In+1=2
Answer: Option B. -> 2√2−2
:
B
y=limn→∞[1n+1√n2+n+⋯+1√n2+(n−1)n]
⇒y=limn→∞⎡⎢⎣1n+1n√1+1n+⋯+1n√1+(n−1)n⎤⎥⎦
⇒y=1nlimn→∞⎡⎢⎣1+1√1+1n+⋯+1√1+(n−1)n⎤⎥⎦
y=limn→∞1n∑k=1n1√1+(k−1)n,Putk−1n=xand1n=dx
⇒y=limn→∞∫n−1n0dx√1+x=limn→∞2[√1+x](n−1n)0
⇒y=2limn→∞[√2n−1n−1]=2limn→∞√2n−1n−2
⇒y=2limn→∞√2−1n−2=2√2−2
:
B
y=limn→∞[1n+1√n2+n+⋯+1√n2+(n−1)n]
⇒y=limn→∞⎡⎢⎣1n+1n√1+1n+⋯+1n√1+(n−1)n⎤⎥⎦
⇒y=1nlimn→∞⎡⎢⎣1+1√1+1n+⋯+1√1+(n−1)n⎤⎥⎦
y=limn→∞1n∑k=1n1√1+(k−1)n,Putk−1n=xand1n=dx
⇒y=limn→∞∫n−1n0dx√1+x=limn→∞2[√1+x](n−1n)0
⇒y=2limn→∞[√2n−1n−1]=2limn→∞√2n−1n−2
⇒y=2limn→∞√2−1n−2=2√2−2