Range of the function f (x)= -lx+1l is (a) [0, infinity ) (b) ( - infinity , 0]
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x l + lx-1l=
Algebraic approach:
Let's check in which ranges of expression holds true:
Two check points for : 0 and 1 (x=0 and x-1=0, x=1), thus three ranges to check:
A. --> --> , not good as we are checking for ;
B. --> --> , which is true. This means that in this range given equation holds true for all x-es;
C. --> --> , not good as we are checking for .
So we got that the equation holds true only in the range .
(1) . Not sufficient.
(2) . Not sufficient.
(1)+(2) gives us the range , which is exactly the range for which given equation holds true. Sufficient.
Here, f:[0,∞)→[0,∞) i.e, domain is [0,∞) and codomain is [0,∞)
For one-one
f(x)=1+x
xf,(x)=
(x)= (1+x)21
>0,∀x∈[0,∞)
∴f(x) is increasing in this domain. Thus f(x) is one-one in its domain
For onto (we find range)
f(x)= 1+x
x
i.e. y= 1+x
⇒y+yx=x
⇒x=
1−y
y
⇒x=
1−y
y
≥0 as x≥0
∴0≤y
=1 and y<1
∴ Range
= Codomain
∴f(x) is one-one but not onto
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