Class 10 Optional Mathematics Solution
Algebra
Exercise: 1 'A'
1.
Given functions are:
f(x) = 3x - 4, h(x) = x + 3, g(x) = -2x + 1
a.
Here, fh = f(h(x)) = f(x + 3)
= 3 (x + 3) - 4
= 3x + 9 - 4 = 3x + 5
b.
Here, hh = h(h(x)) = h(x + 3)
= (x + 3) + 3 = x + 6
c.
Here, gh(f)(x) = gh(f(x))
= gh(3x - 4)
= g [h (3x - 4)]
= g [(3x - 4) + 3]
= g(3x - 1)
= -2(3x - 1) + 1
= -6x + 3
d.
Here, f[g(h)](x) = f[g(h(x))]
= f[g(x + 3)]
= f[-2(x + 3) + 1]
= f(-2x - 6 + 1) = f(-2x - 5)
= 3(-2x - 5) - 4
= -6x - 15 - 4 = -6x - 19
2.
Here, from question no. 1 ,
f(x) = 3x - 4 , h(x) = x + 3 and g(x) = -2x + 1
a.
From 1"A",
fh = fh(x) = 3x + 5 [fh(x) = 3x + 5]
Here, putting x = 2,
fh(2) = 3.2 + 5 = 6 + 5 = 11
b.
From 1"B",
hh = x + 6[
so, hh(x) = x + 6
Here, putting x = 2,
hh(2) = 2 + 6 = 8
c.
From 1"D",
f(gh) = fh(x) = -6x - 19
f(gh)(x) = -6x - 19
Here, putting x = 3,
f(gh)(3) = -6.3 - 19 = -18 - 19 = -37
d.
f(hh) = fh(h) [h(x)= x + 3]
= fh(x + 3)
= fh{(x + 3)+ 3}
= f(x + 6) = 3(x + 6) - 4 [f(x) = 3x - 4]
= 3x + 18 - 4 = 3x + 14
So, f(hh)(x) = 3x + 14
Here, putting x = -5,
f(hh)(-5) = 3 - 5 + 14= -15 + 14 = -1
3.
Here, given functions are:
f(x) = $\frac{1}{x}$ ; x θ R , x θ 0.
a.
Here, ff(x) = f[f(x)] = f ($\frac{1}{x}$< /FONT>)
= $\frac{1}{{\frac{1}{x}}} = x$
So, f(x) = $\frac{1}{x}$
So, ff(2) = 2
b.
Here, ff(x) = x [ from "A"]
so, ff(3) = 3
c.
Here, From "A".
ff(x) = x
so, ff(-3) = -3
d.
Here, from "A",
ff(x) = x
4.
Here, given;
f(x) = x3 and g(x) = x2
Here, fg(x) = f[g(x)]
= f(x2) [g(x) = x2]
= (x2)3 [f(x) = x3]
=x6
Again, gf(x) = g[f(x)]
= g(x3) [f(x) = x3]
= (x3)2 [g(x) = x2]
=x6
5.
a.
Here, given function is, f = {(1,1), (2,2), (3,3)}
Now, interchanging the position of domain and range of the function to get a inverse function f-1< /SUP>. Now, since f is a one-one union.
(f-1) = {(1,1), (2,2), (3,3)}
b.
Here, given function is, f = {(x,y):y = x, x, y θ R}
Now, interchanging the position of domain and range of the function to get a inverse function f-1< /SUP>. Now, since f is a one-one union.
(f-1) = {(y,x): x = y, x, y θ R}
c.
Here, given function is, f = {(x,2x + 1): x θ R}
Here, let us suppose, y = 2x + 1
Now, interchanging the position of x and y.
x = 2y + 1
or, x - 1 =2y [ y =$\: \frac{{x - 1}}{2}]$
now, inverse of f is;
(f-1) = {(x,$\: \frac{{x - 1}}{2}$): x θ R}
d.
Here, given function is, f = {(x,y): y =$\: \frac{1}{x}\: ,\: $x θ R, xθ0}
Here, y =$\: \frac{1}{x}$
Now, interchanging the position of x and y.
So, x = $\frac{1}{y}$ and y = $\frac{1}{x}$
Now, the inverse of function f is:
f-1 = {(y,x): x =$\: \frac{1}{y}\: ,\: $x θ R, yθ0}
6.
a.Here the given function is:
f:x θ 4x, or f(x) = 4x
Let us suppose, y = 4x
Now, interchanging the positions of x and y.
x= 4y and y = $\frac{x}{4}$
Now, inverse of the function f-1(x) = $\frac{x}{4}$
b.
Here, the given function is:
g:x 3x + 4, or g(x) = 3x + 4
Let us suppose, y = 3x + 4
Now, interchanging the positions of x and y.
x= 3y + 4
or, x - 4 = 3y
so, y = $\frac{{x - 4}}{3}$
Now, inverse of the function g-1: x = $\frac{{x - 4}}{3}$
So, g-1(x) = $\frac{{x - 4}}{3}$
c.
Here, the given function is:
h:x-> $\frac{{x\: + \: 3}}{2}$, or h(x) = $\frac{{x\: + \: 3}}{2}$
Let us suppose, y = $\frac{{x\: + \: 3}}{2}$
Now, interchanging the positions of x and y.
x = $\frac{{y\: + \: 3}}{2}$
or, 2x = y + 3
so, y = 2x - 3
Now, inverse of the function h-1: x = 2x - 3
So, h-1(x) = 2x - 3
d.
Here, the given function is:
k:x-> $\frac{{2x\: + \: 5}}{{x + 2}}$, or k(x) = $\frac{{2x\: + \: 5}}{{x + 2}}$
Let us suppose, y =$\: \frac{{2x\: + \: 5}}{{x + 2}}$
Now, interchanging the positions of x and y.
x = $\frac{{2y\: + \: 5}}{{y + 2}}$
or, xy + 2x = 2y + 5
or, y(x - 2) = 5 - 2x
so, y = $\frac{{5 - 2x\: }}{{x - 2}}$
Now, inverse of the function h-1: x = 2x - 3
So, k-1(x) = $\frac{{5 - 2x\: }}{{x - 2}}$; xθ 2
7.
a.
Here, according to question 6(A) ,
f(x) = 4x and f-1(x) = $\frac{x}{4}$
so, ff-1(x) = f[f-1(x)] = f ($\frac{x}{4}$) = 4$\left({\frac{x}{4}} \right)$
b.
Here, according to question 6(A) ,
g(x) = 3x + 4 and h-1(x) = $2x - 3$
so,gh-1(x) = g[h-1(x)] = g(2x - 3)
= 3(2x - 3) + 4
= 6x - 9 + 4
= 6 x- 5
8.
Here, given;
The inverse of f(x) = x + 2 is f-1 (x) = x - 2
a.
Here,f(-2)
Now, let us put x = -2 in f(x) = x + 2
So, f(-2) = -2 + 2 = 0
b.
Here, f-1(-2)
Now, let us put x = -2 in f(x) = x + 2
So, f-1(-2) = -2 - 2 = -4
c.
Here,
Now, let us put x = 4 in f(x) = x + 2
So, f (4) = 4 + 2 = 6
d.
Here,
Now, let us put x = -4 in f-1(x) = x - 2
So, f (4) = -4 - 2 = -6
e.
Here, f(x -2)
Now, let us put x = -4 in f (x + 2) = (x - 2) + 2 = x - 2 + 2 = x
So, f (x-2) = x
f.
Here, f-1(x +2)
Now, let us put x = -4 in f-1 (x - 2) = (x + 2) - 2 = x
So, f-1 (x-2) = x
9.
Here,
y = x + 1 , x θ N
y = x + 1, x θ Z and
y = x + 1, x θ R
Here, every function is in f(x) = mx + c.
so,
a. The given functions are linear functions.
b. Here given; (i) y - 5, x θ N, (ii) y = 5, x θ Z (iii) y = 5, x θ R.
Since y = fx = c, the functions are constant functions.
c.
Here given,
(i) y = x, x θ N
(ii) y = x, x θ Z
(iii) y = x, x θ R
Here, every function is in the form of y = f(x) = x
So, all the functions are 1 to 1 functions.
10.
To draw the graph of y = sinθ and y = sin3θ, θ is divided from 0° to 180° in the graph. And their respective trigonometric values are also added
a.
In the equation y = sin2θ
θ°=x |
0° |
15° |
30° |
45° |
60° |
75° |
90° |
105° |
120° |
135° |
150° |
165° |
180° |
2θ |
0° |
30° |
60° |
90° |
120° |
150° |
180° |
210° |
240° |
270° |
300° |
330° |
360° |
Sin2θ=y |
0 |
0.5 |
0.87 |
1 |
0.87 |
0.5 |
0 |
-0.5 |
-0.87 |
-1 |
-0.87 |
-0.5 |
0 |
Now, plotting y = sin2θ in graph. We get,
b.
y = sin3θ
To draw the graph of y = sinθ and y = sin3θ, θ is divided from 0° to 180° in the graph. And their respective trigonometric values are also added
In the equation y = sin3θ,
θ°=x |
0° |
15° |
30° |
45° |
60° |
75° |
90° |
105° |
120° |
135° |
150° |
165° |
180° |
2θ |
0° |
45° |
90° |
135° |
180° |
225° |
270° |
315° |
360° |
405° |
450° |
495° |
540° |
Sin2θ=y |
0 |
0.71 |
1 |
0.71 |
0 |
-0.71 |
-1 |
-0.71 |
0 |
0.71 |
1 |
0.71 |
0 |
Now, plotting y = sin2θ in graph. We get,