

NCERT Solutions for Class 12 Maths Chapter 6 Miscellaneous Exercise
Question 1. Using differentials, find the approximate value of each of the following up to 3 places of decimal:
(i) √25.3 (ii)√49.5 (iii)√0.6 (iv)(0.009) 1/3 (v)(0.999) 1/10 (vi) (15) 1/4 (vii) (26) 1/3 (viii) (255)1/4 (ix) (82) 1/4 (x) (401)1/2 (xi) (0.0037)1/2 (xii) (26.57) 1/3 (xiii) (81.5) 1/4 (xiv) (3.968) 3/2 (xv) (32.15) 1/5 Solution : (i) √25.3
(ii)
√49.5
(iii)
√0.6
(iv)
(0.009)
1/3
(v)
(0.999)
1/10
(vi)
(15)
1/4
(vii)
(26)
1/3
(viii)
(255)1/4
(ix)
(82)
1/4
(x)
(401)1/2
(xi)
(0.0037)1/2
(xii)
(26.57)
1/3
(xiii)
(81.5)
1/4
(xiv)
(3.968)
3/2
(xv) (32.15)
1/5
NCERT Solutions for Class 12 Maths Chapter 6 Exercise 6.1
Question 2. Find the approximate value off (2.01), where f(x) = 4x 2 + 5x + 2 Solution :
Hence, the approximate value of
f
(2.01) is 28.21.
NCERT Solutions for Class 12 Maths Chapter 6 Exercise 6.2
Question 3. Find the approximate value of f (5.001), wheref (x) =x 3 − 7x 2 + 15. Solution :
Hence, the approximate value of
f
(5.001) is −34.995.
NCERT Solutions for Class 12 Maths Chapter 6 Exercise 6.3
Question 4. Find the approximate change in the volume of a cube of side x meters caused by increasing the side by 1%. Solution :
Hence, the approximate change in the volume of the cube is 0.03
x
3
m
3
.
Question
5. Find the approximate change in the surface area of a cube of side x meters caused by decreasing the side by 1%.
Solution :
The surface area of a cube (
S)
of side
x
is given by
S
= 6
x
2
.
Hence, the approximate change in the surface area of the cube is 0.12
x
2
m
2
.
NCERT Solutions for Class 12 Maths Chapter 6 Exercise 6.5
Question 6. If the radius of a sphere is measured as 7 m with an error of 0.02 m, then find the approximate error in calculating its volume. Solution : Let r be the radius of the sphere and Δ r be the error in measuring the radius. Then, r = 7 m and Δ r = 0.02 m Now, the volume V of the sphere is given by,
Hence, the approximate error in calculating the volume is 3.92 π m
3
.
Question
7. If the radius of a sphere is measured as 9 m with an error of 0.03 m, then find the approximate error in calculating its surface area.
Solution :
Let
r
be the radius of the sphere and Δ
r
be the error in measuring the radius.
Then,
r
= 9 m and Δ
r
= 0.03 m
Now, the surface area of the sphere (
S)
is given by,
S
= 4πr
2
Hence, the approximate error in calculating the surface area is 2.16π m
2
.
Question
8. Iff (x) = 3x
2
+ 15x + 5, then the approximate value of f (3.02) is
A. 47.66
B. 57.66
C. 67.66
D.77.66
Solution :
Therefore, option (D) is correct.
Question
9. The approximate change in the volume of a cube of sidex metres caused by increasing the side by 3% is
A. 0.06x
3
m
3
B. 0.6x
3
m
3
C. 0.09x
3
m
3
D.0.9x
3
m
3
Solution :
The volume of a cube (
V
) of side
x
is given by
V
=
x
3
.
Therefore, option (C) is correct.
