CBSE NCERT Solutions for Class 10 Mathematics Chapter 8
Class- X-CBSE-Mathematics
Introduction to Trigonometry
CBSE NCERT Solutions for Class 10 Mathematics Chapter 8
Back of Chapter Questions
1. In ABC, right-angled at B, AB = 24 cm, BC = 7 cm. Determine: (i) sin A , cos A (ii) sin C , cos C Solution: In ABC, apply Pythagoras theorem AC2 = AB2 + BC2 = (24)2 + (7)2 = 625
AC = 625 = 25 cm
(i)
sin A = Side opposite to A = BC
hypotenuse
AC
7 =
25
Side adjacent to A AB cos A = hypotenuse = AC
24 = 25
(ii)
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Class- X-CBSE-Mathematics
Introduction to Trigonometry
Side opposite to C AB 24 sin C = hypotenuse = AC = 25
Side adjacent to C BC 7
cos C =
==
hypotenuse
AC 25
2. In Fig., find tan P - cot R .
Solution: Apply Pythagoras theorem in PQR PR2 = PQ2 + QR2 (13)2 = (12)2 + QR2 169 = 144 + QR2 25 = QR2 QR = 5
Side opposite to P QR tan P = Side adjacent to P = PQ
5 =
12 Side adjacent to R QR
cot R = Side opposite to R = PQ 5
= 12 55
tan P - cot R = 12 - 12 = 0
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Class- X-CBSE-Mathematics
Introduction to Trigonometry
3. If sin A = 3, calculate cos A and tan A.
4
Solution: Let us assume that ABC is a right triangle, right angled at vertex B.
Given that 3
sin A = 4 sin A = Side opposite to A
hypotenuse
BC 3 AC = 4 Let BC and AC be 3R and 4R respectively, where R is any positive number. In ABC, apply Pythagoras theorem AC2 = AB2 + BC2 (4 R)2 = AB2 + (3 R)2 16 R2 - 9 R2 = AB2 7 R2 = AB2
AB = 7R Side adjacent to A
cos A = hypotenuse
= AB = 7R = 7 AC 4R 4 Side opposite to A
tan A = Side adjacent to A
BC 3R 3 = AB = 7R = 7 4. Given 15 cot A = 8, find sin A and sec A. Solution: Let us assume that ABC is a right triangle, right angled at vertex B.
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Class- X-CBSE-Mathematics
Introduction to Trigonometry
Side adjacent to A cot A = Side opposite to A
AB =
BC cot A = 8 (given)
15
AB 8 BC = 15 Let AB and BC be 8R and 15R respectively, where R is a positive number.
Now applying Pythagoras theorem in ABC AC2 = AB2 + BC2
= (8R)2 + (15R)2
= 64 R2 + 225 R2
= 289 R2
AC = 17 R
Side opposite to A BC
sin A =
=
hypotenuse
AC
15 R 15 = 17 R = 17
hypotenuse sec A =
Side adjacent to A
AC 17 = AB = 8
5.
Given
sec
=
13,
12
calculate
all
other
trigonometric
ratios.
Solution:
Let us assume that ABC is a right angled triangle, right angled at vertex B.
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Class- X-CBSE-Mathematics
Introduction to Trigonometry
hypotenuse sec = Side adjacent to B
13 AC 12 = AB
Let AC and AB be 13R and 12R, where R is a positive number.
Now applying Pythagoras theorem in ABC
(AC)2 = (AB)2 + (BC)2
(13 R)2 = (12 R)2 + BC2
169 R2 = 144 R2 + BC2
25 R2 = BC2
BC = 5R
Side opposite to BC 5R 5
sin =
hypotenuse
== = AC 13R 13
Side adjacent to AB 12R 12 cos = hypotenuse = AC = 13R = 13
Side opposite to BC 5R 5 tan = Side adjacent to = AB = 12R = 12
Side adjacent to AB 12R 12 cot = Side opposite to = BC = 5R = 5
hypotenuse
AC 13R 13
coses = Side opposite to = BC = 5R = 5
6. If A and B are acute angles such that cos A = cos B, then show that A = B.
Solution:
Let us assume a right triangle, right angled at vertex C.
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