1
COMEDK 2021
MCQ (Single Correct Answer)
+1
-0

The solution of the differential equation $$y{{dy} \over {dx}} = x\left[ {{{{y^2}} \over {{x^2}}} + {{\phi \left( {{{{y^2}} \over {{x^2}}}} \right)} \over {\phi '\left( {{{{y^2}} \over {{x^2}}}} \right)}}} \right]$$ is (where, C is a constant)

A
$$\phi \left( {{{{y^2}} \over {{x^2}}}} \right) = Cx$$
B
$$x\phi \left( {{{{y^2}} \over {{x^2}}}} \right) = C$$
C
$$\phi \left( {{{{y^2}} \over {{x^2}}}} \right) = C{x^2}$$
D
$${x^2}\phi \left( {{{{y^2}} \over {{x^2}}}} \right) = C$$
2
COMEDK 2021
MCQ (Single Correct Answer)
+1
-0

The solution of the differential equation $$(1 + {y^2}) + (x - {e^{{{\tan }^{ - 1}}y}}){{dy} \over {dx}} = 0$$ is

A
$$2x{e^{{{\tan }^{ - 1}}y}} = {e^{2{{\tan }^{ - 1}}y}} + C$$
B
$$x{e^{{{\tan }^{ - 1}}y}} = {\tan ^{ - 1}}y + C$$
C
$$x{e^{2{{\tan }^{ - 1}}y}} = {e^{{{\tan }^{ - 1}}y}} + C$$
D
$$(x - 2) = C{e^{ - {{\tan }^{ - 1}}y}}$$
3
COMEDK 2021
MCQ (Single Correct Answer)
+1
-0

The value of $$1\,.\,1! + 2\,.\,2! + 3\,.\,3! + \,...\, + \,n\,.\,n!$$ is

A
$$(n + 1)!$$
B
$$(n + 1)! + 1$$
C
$$(n + 1)! - 1$$
D
None of these
4
COMEDK 2021
MCQ (Single Correct Answer)
+1
-0

The sum of the series $$(1 + 2) + (1 + 2 + {2^2}) + (1 + 2 + {2^2} + {2^3}) + ....$$ upto $$n$$ terms is

A
$${2^{n + 2}} - n - 4$$
B
$$2({2^n} - 1) - n$$
C
$${2^{n + 1}} - n$$
D
$${2^{n + 1}} - 1$$
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