Class 12th

We have, f(x) = x + sin 2x ,x ∈ [0, 2π].

f(x) = 1 + 2cos 2x

At f(x) = 0

1 + 2 cos2x = 0

$\Rightarrow cos2x=-\frac{1}{2}=-cos\frac{\pi }{3}=cos\pi -\frac{\pi }{3}=cos\frac{2\pi }{3}$

$\therefore 2x=2n\pi \pm \frac{2\pi }{3},n=1,2,3.$

$\Rightarrow x=n\pi \pm \frac{2\pi }{3}$

$n=0,x=\pm \frac{\pi }{3}\to x=\frac{\pi }{3}\in \left[0,2\pi \right].$

$n=1,x=\pi \pm \frac{\pi }{3}\to x=\pi +\frac{\pi }{3}and\pi -\frac{\pi }{3}$

$=\frac{4\pi }{3}ad\frac{2\pi }{3}\in [0,2\pi ]$

$n=2,x=2\pi \pm \frac{\pi }{3}\to x=2\pi +\frac{\pi }{3}ad2\pi -\frac{\pi }{3}.$

$\Rightarrow x=\frac{51}{3}\in [0,2\pi ].$

Hence, $x=\frac{\pi }{3},\frac{2\pi }{3},\frac{4\pi }{3}and\frac{5\pi }{3}$

Missing

At $x=\frac{\pi }{3},f\left(\frac{\pi }{3}\right)=\frac{\pi }{3}+sin\frac{2\pi }{3}=1.05+$ $sin\left(\pi -\frac{\pi }{3}\right)=1.05+sin\frac{\pi }{3}$

$=1.05+\surd 3/2$

= 1.05 + 0.87

= 1.92

At $x=\frac{2\pi }{3},f\left(\frac{2\pi }{3}\right)=\frac{2\pi }{3}+sin2*\frac{2\pi }{3}$ $=2.10+sin\left(\pi +\frac{\pi }{3}\right)$

$=2.10-sin\frac{\pi }{3}=2,10-0.87$

= 1.23

At $x=\frac{4\pi }{3},f\left(\frac{4\pi }{3}\right)=\frac{4\pi }{3}+sin2*\frac{4\pi }{3}=4\cdot 2+sin\left(3x-\frac{\pi }{3}\right)$

$=4.2+sin\frac{\pi }{3}=4.2+0.87.$

=5.07.

At $x=\frac{5\pi }{3},f\left(\frac{5\pi }{3}\right)=\frac{5\pi }{3}+sin2*\frac{5\pi }{3}=5.25+sin\left(3x+\frac{\pi }{3}\right)$

$=5\cdot 25-sin\frac{1}{3}$

= 5.25 - 0.87 = 4.38

At and points,

f(0) = 0 + sin2 * 0 = 0

f(2π) = 2π + sin 2 * 2π = 6.2 + 0 = 6.28

∴Maximum value of f(x) = 6.28 at x = 2π and

minimum value of f(x) = 0 at x= 0

We have, f (x) = x⁴- 62x² + ax + 9, x∈  [0, 2].

$\Rightarrow$ f (x) = 4x³- 124x + a

∴f (x) active its maxⁿ value at x = 1∈ [0, 2]

∴f (1) = 0.

4 (1)³- 124 (1) + a = 0

$\Rightarrow$ a = 124 - 4 = 120.

∴a = 120

We have, f (x) =2x³- 24x + 107, x [1,3]

f (x) = 6x²- 24.

At f (x) = 0

6x²- 24= 0

$\Rightarrow x^2=\frac{24}{6}=4$

x = ±2. ->x = 2 ∈ [1, 3].

So, f (2) = 2 (2)³- 24 (2) + 107 = 16 - 48 + 107 = 75.

f (1) = 2 (1)³- 24 (1) + 107 = 2 - 24 + 107 = 85.

f (3) = 2 (3)³- 24 (3) + 107 = 54 - 72 + 107 = 89

∴ Maximum value of f (x) in interval [1, 3] is 89 at x = 3.

When x ∈  [ -3, -1]

From f (x) = 0

x = -2 ∈ [ -3, -1]

So, f (- 2) = 2 (- 2)³- 24 (- 2) + 107 = - 16 + 48 + 107 = 139.

f (- 3) = 2 (- 3)³- 24 (- 3) + 107 = - 54 + 72 + 107 = 125.

f (- 1) = 2 (- 1)³- 24 (- 1) + 107 = - 2 + 24 + 107 = 129.

∴ Maximum value of f (x) in interval [ -3, -1] is 139 at x = -2.

We have, f (x) = sin x + cos x.

f (x) = cos x - sin x.

At f (x) = 0

cosx - sin x = 0

sinx = cos x

$\Rightarrow \frac{sinx}{cosx}=1.$

$\Rightarrow tanx=1=tan\frac{\pi }{4}$

$\Rightarrow x=\frac{\pi }{4}orx=n\pi +\frac{\pi }{4}.$

At $x=\frac{\pi }{4}+n\pi$ ,

$f\left(n\pi +\frac{\pi }{4}\right)=sin\left(n\pi +\frac{\pi }{4}\right)+cos\left(nx+\frac{\pi }{4}\right).$

$={(-1)}^{x}sin\frac{\pi }{4}+{(-1)}^{n}sin\frac{\pi }{4}.$

We have, f(x) = sin 2x, x ∈ [0, 2π],

f(x) = 2cos 2x.

At f(x) = 0.

2 cos 2x = 0

cos 2x = 0

$\Rightarrow 2x=(2x+1)\frac{\pi }{2},x=0,1,2,3.$

$\Rightarrow x=(2x+1)\frac{\pi }{4}.$

$x=\frac{\pi }{4},\frac{3\pi }{4},\frac{5\pi }{4},\frac{7\pi }{4},\in \left[0,2\pi \right]$

$\therefore f\left(\frac{\pi }{4}\right)=sin\frac{2\pi }{4}=sin\frac{\pi }{2}=1$ .

$f\left(\frac{3\pi }{4}\right)=sin2\left(\frac{3\pi }{4}\right)=$ $sin\frac{3\pi }{2}$ $f\left(\frac{7\pi }{4}\right)$

$=sin\left(\pi +\frac{\pi }{2}\right)=$ $=sin2*\frac{7\pi }{4}$

$=-sin\frac{\pi }{2}$ $=sin\frac{7\pi }{2}$

= 1. $=sin3\pi +\frac{\pi }{2}$

$f\left(\frac{5\pi }{4}\right)=sin2*\left(\frac{5\pi }{4}\right)=sin\frac{5\pi }{2}=sin\left(2x+\frac{\pi }{4}\right)$ $=-sin\frac{\pi }{2}$

$=sin\frac{\pi }{4}=1$ = 1.

f(0) = sin 2(0) = sin 0 = 0

f(2π) = sin 2(2π) = sin 4π = 0

Hence, the points of maximum $xf\mathrm{x\; are.}$

$(\frac{\pi }{4},2)and\left(\frac{5\pi }{4},1\right).$

We have, f (x) = 3x⁴- 8x³ + 12x²- 48x + 25, x ∈  [0, 3].

f (x) = 12x³- 24x² + 24x - 48.

At f (x) = 0.

12x³- 24x² + 24x - 48 = 0.

x³- 2x² + 2x - 4 = 0

x² (x - 2) + 2 (x - 2) = 0

(x - 2) + (x² + 2) = 0

x = 2 ∈ [0, 3] or x = $\pm \surd -2$ which is not possible as

∴f (x) = 3 (2)⁴- 8 (2)³ + 12 (2)²- 4 (2) + 25.

=48 - 64 + 48 - 96 + 25.

= -39.

f (0) =3 (0)⁴- 8 (0)³ + 12 (0)²- 48 (0) + 25.

= 25.

f (3) = 3 (3)⁴- 8 (3)³ + 12 (3)²- 48 (3) + 25.

= 243 - 216 + 108 - 144 + 25

= 16.

Maximum value of f (x) = 25 at x = 0.

and minimum value of f (x) = -39 at x = 2.

We have, p (x) = 41 -f2x - 18x².

P (x) = - 72 - 36x

P (x) = -36

At extreme point,

- 72 - 36x = 0

$\Rightarrow$ $x=\frac{-72}{36}=-2$ .

At x = - 2, p" (x) = - 36 < 0.

∴x = -2 is a point of local maximum and the value of local

Maximum is given by P (2) = 41 - 72 (- 2) - 18 (- 2)²

41 + 144 - 72 = 113 units.

(i) We have, f (x) = e^x

$\Rightarrow$ f (x) = e^x.

$\Rightarrow f^{\prime }(x)=e^{x.}$

At, extreme points,

f (x) = 0

$\Rightarrow$ e^x = 0 which has no real 'a' value

∴f (x) has with maximum or minima

(ii) g (x) = log x

A (ii)

We have, g (x) = log x,

$\Rightarrow$ g (x) = $\frac{1}{x}$

At extreme points,

g (x) = 0

$\to \frac{1}{x}=0.$

$\Rightarrow$ 1 = 0 which is not true.

∴g (x) was value minima or maxima

(iii) h (x) = x³ + x² + x + 1.

A (iii)

We have, h (x) = x³ + x² + x + 1.

h (x) = 3x² + 2x + 1

At extreme points,

h (x) = 0

$\Rightarrow$ 3x² + 2x + 1 = 0