1
JEE Main 2021 (Online) 1st September Evening Shift
+4
-1
The range of the function,

$$f(x) = {\log _{\sqrt 5 }}\left( {3 + \cos \left( {{{3\pi } \over 4} + x} \right) + \cos \left( {{\pi \over 4} + x} \right) + \cos \left( {{\pi \over 4} - x} \right) - \cos \left( {{{3\pi } \over 4} - x} \right)} \right)$$ is :
A
$$\left( {0,\sqrt 5 } \right)$$
B
[$$-$$2, 2]
C
$$\left[ {{1 \over {\sqrt 5 }},\sqrt 5 } \right]$$
D
[0, 2]
2
JEE Main 2021 (Online) 31st August Evening Shift
+4
-1
Let f : N $$\to$$ N be a function such that f(m + n) = f(m) + f(n) for every m, n$$\in$$N. If f(6) = 18, then f(2) . f(3) is equal to :
A
6
B
54
C
18
D
36
3
JEE Main 2021 (Online) 27th July Evening Shift
+4
-1
Let f : R $$\to$$ R be defined as $$f(x + y) + f(x - y) = 2f(x)f(y),f\left( {{1 \over 2}} \right) = - 1$$. Then, the value of $$\sum\limits_{k = 1}^{20} {{1 \over {\sin (k)\sin (k + f(k))}}}$$ is equal to :
A
cosec2(21) cos(20) cos(2)
B
sec2(1) sec(21) cos(20)
C
cosec2(1) cosec(21) sin(20)
D
sec2(21) sin(20) sin(2)
4
JEE Main 2021 (Online) 25th July Evening Shift
+4
-1
Consider function f : A $$\to$$ B and g : B $$\to$$ C (A, B, C $$\subseteq$$ R) such that (gof)$$-$$1 exists, then :
A
f and g both are one-one
B
f and g both are onto
C
f is one-one and g is onto
D
f is onto and g is one-one
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