Practice Set 8.2 Geometry 9th Std Maths Part 2 Answers Chapter 8 Trigonometry
ii. sin θ = …..(i) [Given]
In right angled ∆ABC, ∠C = θ.
Let the common multiple be k.
AB = 11k and AC = 61k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
∴ (61k)2= (11k)2+ BC2
∴ 3721k2= 121k2+ BC2
∴ BC2= 3721k2– 121k2= 3600k2
BC = ...[Taking square root of both sides]
= 60k
iii. tan θ = 1 = ..(i) [Given]
In right angled ∆ABC,
∠C = θ.
Let the common multiple be k.
∴ AB = 1k and BC = 1k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
= K2+ K2
= 2K2
∴ AC =
iv. sin θ = ..(i) [Given]
In right angled ∆ABC,
∠C = θ.
Let the common multiple be k.
∴ AB = 1k and BC = 2k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
∴ 2K2= K2+ BC2
∴ 4K2= K2+ BC2
∴ BC2= 4K2– K2= 3K2
∴ BC = ...[Taking square root of both sides]
=
v. cos θ = ..(i) [Given]
In right angled ∆ABC,
∠C = θ.
Let the common multiple be k.
∴ AB = 1k and BC = √3k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
∴ (√3K)2= AB2+ K2
∴ 3K2= 3K2– K2= 2K2
∴ AB = ...[Taking square root of both sides]
AB = √2K
vi. cos θ = ..(i) [Given]
In right angled ∆ABC,
∠C = θ.
Let the common multiple be k.
∴ AB = 21k and BC = 20k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
= (21)K2+ (20K)2
= 441K2– 4002
= 841K2
∴ AB = ...[Taking square root of both sides]
= 29K
vii. tan θ = ..(i) [Given]
In right angled ∆ABC,
∠C = θ.
Let the common multiple be k.
∴ AB = 8k and BC = 15k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
= (8)K2+ (15K)2
= 64K2– 2252
= 289K2
∴ AC = ...[Taking square root of both sides]
= 17K
viii. sin θ = ..(i) [Given]
In right angled ∆ABC,
∠C = θ.
Let the common multiple be k.
∴ AB = 3k and AC = 5k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
∴ (5)K2= (3)K2+ BC2
∴ 25K2= 9K2– 2252
∴ BC2= 25K2– 9K2
∴ BC = ...[Taking square root of both sides]
= 4K
ix. tan θ = ..(i) [Given]
In right angled ∆ABC,
∠C = θ.
Let the common multiple be k.
∴ AB = 1k and AC = 2√2 k
Now, AC2= AB2+ BC2…[Pythagoras theorem]
= K2+ (2√2 k )2
= K2– 2252
= 25K2+ 8K2
= 9K2
∴ AC = ...[Taking square root of both sides]
= 3K
ii. tan260° + 3 sin260°
iii. 2 sin 30° + cos 0° + 3 sin 90°
2 sin 30° + cos0° + 3 sin 90° = 2 () + 1 + 3(1)
= 1 + 1 + 3
∴ 2 sin 30° + cos 0° + 3 sin 90° = 5
iv.
v. cos245° + sin230°
vi. cos 60° x cos 30° + sin 60° x sin 30°
Maharashtra Board Class 9 Maths Chapter 8 Trigonometry Practice Set 8.2 Intext Questions and Activities
iii. Let ∠P = θ = 30°
∴ ∠R = 90° – 30°
sin 30° = cos (90° – 30°) … [From (i) and (ii)]
sin 30° = cos 60°
iv. cos 30° = sin (90° – 30°) = sin 60°
∴ cos 30° = sin (90° – 30°).,.[From (i) and (ii)]
∴ cos 30° = sin 60°
ii. If θ = 90°,
L.H.S.= sin2θ +cos2θ
= sin290° + cos290°
= 1 + 0 … [ ∵ sin 90° = 1, cos 90° = 0]
= 1
= R.H.S.
∴ sin2θ + cos2θ = 1