1. Ans:(A) 123
Given function:
![f(x) = 8x^2 + 11x](https://tex.z-dn.net/?f=f%28x%29%20%3D%208x%5E2%20%2B%2011x)
The derivative would be:
![\frac{d}{dx} f(x) = \frac{d}{dx}(8x^2 + 11x)](https://tex.z-dn.net/?f=%20%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%288x%5E2%20%2B%2011x%29)
=>
![\frac{d}{dx} f(x) = \frac{d}{dx}(8x^2) + \frac{d}{dx}(11x)](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%288x%5E2%29%20%2B%20%5Cfrac%7Bd%7D%7Bdx%7D%2811x%29)
=>
![\frac{d}{dx} f(x) = 2*8(x^{2-1}) + 11](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%202%2A8%28x%5E%7B2-1%7D%29%20%2B%2011)
=>
![\frac{d}{dx} f(x) = 16x + 11](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%2016x%20%2B%2011)
Now at x = 7:
![\frac{d}{dx} f(7) = 16(7) + 11](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%287%29%20%3D%2016%287%29%20%2B%2011)
=>
2. Ans:(B) 3
Given function:
![f(x) =3x + 8](https://tex.z-dn.net/?f=f%28x%29%20%3D3x%20%2B%208)
The derivative would be:
![\frac{d}{dx} f(x) = \frac{d}{dx}(3x + 8)](https://tex.z-dn.net/?f=%20%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%283x%20%2B%208%29)
=>
![\frac{d}{dx} f(x) = \frac{d}{dx}(3x) + \frac{d}{dx}(8)](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%283x%29%20%2B%20%5Cfrac%7Bd%7D%7Bdx%7D%288%29)
=>
![\frac{d}{dx} f(x) = 3*1 + 0](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%203%2A1%20%2B%200)
=>
![\frac{d}{dx} f(x) = 3](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%203)
Now at x = 4:
![\frac{d}{dx} f(4) = 3](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%284%29%20%3D%203)
(as constant)
=>Ans:
![\frac{d}{dx} f(4) =](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%284%29%20%3D)
3
3. Ans:(D) -5
Given function:
![f(x) = \frac{5}{x}](https://tex.z-dn.net/?f=f%28x%29%20%3D%20%5Cfrac%7B5%7D%7Bx%7D%20)
The derivative would be:
![\frac{d}{dx} f(x) = \frac{d}{dx}(\frac{5}{x})](https://tex.z-dn.net/?f=%20%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%28%5Cfrac%7B5%7D%7Bx%7D%29)
or
![\frac{d}{dx} f(x) = \frac{d}{dx}(5x^{-1})](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%285x%5E%7B-1%7D%29)
=>
![\frac{d}{dx} f(x) = 5*(-1)*(x^{-1-1})](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%205%2A%28-1%29%2A%28x%5E%7B-1-1%7D%29)
=>
![\frac{d}{dx} f(x) = -5x^{-2}](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20-5x%5E%7B-2%7D)
Now at x = -1:
![\frac{d}{dx} f(-1) = -5(-1)^{-2}](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28-1%29%20%3D%20-5%28-1%29%5E%7B-2%7D)
=>
![\frac{d}{dx} f(-1) = -5 *\frac{1}{(-1)^{2}}](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28-1%29%20%3D%20-5%20%2A%5Cfrac%7B1%7D%7B%28-1%29%5E%7B2%7D%7D)
=> Ans:
4. Ans:(C) 7 divided by 9
Given function:
![f(x) = \frac{-7}{x}](https://tex.z-dn.net/?f=f%28x%29%20%3D%20%5Cfrac%7B-7%7D%7Bx%7D%20)
The derivative would be:
![\frac{d}{dx} f(x) = \frac{d}{dx}(\frac{-7}{x})](https://tex.z-dn.net/?f=%20%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%28%5Cfrac%7B-7%7D%7Bx%7D%29)
or
![\frac{d}{dx} f(x) = \frac{d}{dx}(-7x^{-1})](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20%5Cfrac%7Bd%7D%7Bdx%7D%28-7x%5E%7B-1%7D%29)
=>
![\frac{d}{dx} f(x) = -7*(-1)*(x^{-1-1})](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%20-7%2A%28-1%29%2A%28x%5E%7B-1-1%7D%29)
=>
![\frac{d}{dx} f(x) = 7x^{-2}](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28x%29%20%3D%207x%5E%7B-2%7D)
Now at x = -3:
![\frac{d}{dx} f(-3) = 7(-3)^{-2}](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28-3%29%20%3D%207%28-3%29%5E%7B-2%7D)
=>
![\frac{d}{dx} f(-3) = 7 *\frac{1}{(-3)^{2}}](https://tex.z-dn.net/?f=%5Cfrac%7Bd%7D%7Bdx%7D%20f%28-3%29%20%3D%207%20%2A%5Cfrac%7B1%7D%7B%28-3%29%5E%7B2%7D%7D)
=> Ans:
5. Ans:(C) -8
Given function:
![f(x) = x^2 - 8](https://tex.z-dn.net/?f=f%28x%29%20%3D%20x%5E2%20-%208)
Now if we apply limit:
![\lim_{x \to 0} f(x) = \lim_{x \to 0} (x^2 - 8)](https://tex.z-dn.net/?f=%20%5Clim_%7Bx%20%5Cto%200%7D%20f%28x%29%20%3D%20%5Clim_%7Bx%20%5Cto%200%7D%20%28x%5E2%20-%208%29)
=>
![\lim_{x \to 0} f(x) = (0)^2 - 8](https://tex.z-dn.net/?f=%5Clim_%7Bx%20%5Cto%200%7D%20f%28x%29%20%3D%20%280%29%5E2%20-%208)
=> Ans:
6. Ans:(C) 9
Given function:
![f(x) = x^2 + 3x - 1](https://tex.z-dn.net/?f=f%28x%29%20%3D%20x%5E2%20%2B%203x%20-%201)
Now if we apply limit:
![\lim_{x \to 2} f(x) = \lim_{x \to 2} (x^2 + 3x - 1)](https://tex.z-dn.net/?f=%20%5Clim_%7Bx%20%5Cto%202%7D%20f%28x%29%20%3D%20%5Clim_%7Bx%20%5Cto%202%7D%20%28x%5E2%20%2B%203x%20-%201%29)
=>
![\lim_{x \to 2} f(x) = (2)^2 + 3(2) - 1](https://tex.z-dn.net/?f=%5Clim_%7Bx%20%5Cto%202%7D%20f%28x%29%20%3D%20%282%29%5E2%20%2B%203%282%29%20-%201)
=> Ans:
7. Ans:(D) doesn't exist.
Given function:
![f(x) = -6 + \frac{x}{x^4}](https://tex.z-dn.net/?f=f%28x%29%20%3D%20-6%20%2B%20%5Cfrac%7Bx%7D%7Bx%5E4%7D%20)
In this case, even if we try to simplify it algebraically, there would ALWAYS be x power something (positive) in the denominator. And when we apply the limit approaches to 0, it would always be either + infinity or -infinity. Hence, Limit doesn't exist.
Check:
![f(x) = -6 + \frac{x}{x^4} \\ f(x) = -6 + \frac{1}{x^3} \\ f(x) = \frac{-6x^3 + 1}{x^3} \\ Rationalize: \\ f(x) = \frac{-6x^3 + 1}{x^3} * \frac{x^{-3}}{x^{-3}} \\ f(x) = \frac{-6x^{3-3} + x^{-3}}{x^0} \\ f(x) = -6 + \frac{1}{x^3} \\ Same](https://tex.z-dn.net/?f=f%28x%29%20%3D%20-6%20%2B%20%5Cfrac%7Bx%7D%7Bx%5E4%7D%20%5C%5C%20f%28x%29%20%3D%20-6%20%2B%20%5Cfrac%7B1%7D%7Bx%5E3%7D%20%5C%5C%20f%28x%29%20%3D%20%5Cfrac%7B-6x%5E3%20%2B%201%7D%7Bx%5E3%7D%20%5C%5C%20Rationalize%3A%20%5C%5C%20f%28x%29%20%3D%20%5Cfrac%7B-6x%5E3%20%2B%201%7D%7Bx%5E3%7D%20%2A%20%5Cfrac%7Bx%5E%7B-3%7D%7D%7Bx%5E%7B-3%7D%7D%20%5C%5C%20f%28x%29%20%3D%20%5Cfrac%7B-6x%5E%7B3-3%7D%20%2B%20x%5E%7B-3%7D%7D%7Bx%5E0%7D%20%5C%5C%20f%28x%29%20%3D%20-6%20%2B%20%5Cfrac%7B1%7D%7Bx%5E3%7D%20%5C%5C%20Same)
If you apply the limit, answer would be infinity.
8. Ans:(A) Doesn't Exist.
Given function:
![f(x) = 9 + \frac{x}{x^3}](https://tex.z-dn.net/?f=f%28x%29%20%3D%209%20%2B%20%5Cfrac%7Bx%7D%7Bx%5E3%7D%20)
Same as Question 7
If we try to simplify it algebraically, there would ALWAYS be x power something (positive) in the denominator. And when we apply the limit approaches to 0, it would always be either + infinity or -infinity. Hence, Limit doesn't exist.
9, 10.
Please attach the graphs. I shall amend the answer. :)
11. Ans:(A) Doesn't exist.
First We need to find out:
![\lim_{x \to 9} f(x)](https://tex.z-dn.net/?f=%20%5Clim_%7Bx%20%5Cto%209%7D%20f%28x%29)
where,
![f(x) = \left \{ {{x+9, ~~~~~x \textless 9} \atop {9- x,~~~~~x \geq 9}} \right.](https://tex.z-dn.net/?f=f%28x%29%20%3D%20%5Cleft%20%5C%7B%20%7B%7Bx%2B9%2C%20~~~~~x%20%5Ctextless%209%7D%20%5Catop%20%7B9-%20x%2C~~~~~x%20%5Cgeq%209%7D%7D%20%5Cright.%20)
If both sides are equal on applying limit then limit does exist.
Let check:
If x
![\textless](https://tex.z-dn.net/?f=%5Ctextless)
9: answer would be 9+9 = 18
If x
![\geq](https://tex.z-dn.net/?f=%20%5Cgeq%20)
9: answer would be 9-9 = 0
Since both are not equal, as
![18 \neq 0](https://tex.z-dn.net/?f=18%20%5Cneq%200)
, hence
limit doesn't exist.
12. Ans:(B) Limit doesn't exist.
Find out:
![\lim_{x \to 1} f(x)](https://tex.z-dn.net/?f=%20%5Clim_%7Bx%20%5Cto%201%7D%20f%28x%29)
where,
![f(x) = \left \{ {{1-x, ~~~~~x \textless 1} \atop {x+7,~~~~~x \textgreater 1} } \right. \\ and \\ f(x) = 8, ~~~~~ x=1](https://tex.z-dn.net/?f=f%28x%29%20%3D%20%5Cleft%20%5C%7B%20%7B%7B1-x%2C%20~~~~~x%20%5Ctextless%201%7D%20%5Catop%20%7Bx%2B7%2C~~~~~x%20%5Ctextgreater%201%7D%20%7D%20%5Cright.%20%5C%5C%20and%20%5C%5C%20f%28x%29%20%3D%208%2C%20~~~~~%20x%3D1%20)
If all of above three are equal upon applying limit, then limit exists.
When x < 1 -> 1-1 = 0
When x = 1 -> 8
When x > 1 -> 7 + 1 = 8
ALL of the THREE must be equal. As they are not equal. 0
![\neq](https://tex.z-dn.net/?f=%20%5Cneq%20)
8; hence,
limit doesn't exist.
13. Ans:(D) -∞
; x = 9
f(x) = 1/(x-9).
Table:
x f(x)=1/(x-9)
----------------------------------------
8.9 -10
8.99 -100
8.999 -1000
8.9999 -10000
9.0 -∞
Below the graph is attached! As you can see in the graph that at x=9, the curve approaches but NEVER exactly touches the x=9 line. Also the curve is in downward direction when you approach from the left. Hence, -∞, x =9 (correct)
14. Ans: -6
s(t) = -2 - 6t
Inst. velocity = ![\frac{ds(t)}{dt}](https://tex.z-dn.net/?f=%20%5Cfrac%7Bds%28t%29%7D%7Bdt%7D%20)
Therefore,
![\frac{ds(t)}{dt} = \frac{ds(t)}{dt}(-2-6t) \\ \frac{ds(t)}{dt} = 0 - 6 = -6](https://tex.z-dn.net/?f=%5Cfrac%7Bds%28t%29%7D%7Bdt%7D%20%3D%20%5Cfrac%7Bds%28t%29%7D%7Bdt%7D%28-2-6t%29%20%5C%5C%20%5Cfrac%7Bds%28t%29%7D%7Bdt%7D%20%3D%200%20-%206%20%3D%20-6)
At t=2,
Inst. velocity = -6
15. Ans: +∞, x =7
f(x) = 1/(x-7)^2.
Table:
x f(x)= 1/(x-7)^2
--------------------------
6.9 +100
6.99 +10000
6.999 +1000000
6.9999 +100000000
7.0 +∞
Below the graph is attached! As you can see in the graph that at x=7, the curve approaches but NEVER exactly touches the x=7 line. The curve is in upward direction if approached from left or right. Hence, +∞, x =7 (correct)
-i