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2 ( 1 − 2 sin 2 θ ) + 3 sin θ = 3 ⟹ 4 sin 2 θ − 3 sin θ + 1 = 0 2(1 - 2\sin^2\theta) + 3\sin\theta = 3 \implies 4\sin^2\theta - 3\sin\theta + 1 = 0 2 ( 1 − 2 sin 2 θ ) + 3 sin θ = 3 ⟹ 4 sin 2 θ − 3 sin θ + 1 = 0 .
Using quadratic formula: sin θ = 3 ± 9 − 16 8 \sin\theta = \frac{3 \pm \sqrt{9-16}}{8} sin θ = 8 3 ± 9 − 16 . No real solutions for sin θ \sin\theta sin θ .
Correction check: 2 cos ( 2 θ ) + 3 sin θ = 3 ⟹ 2 ( 1 − 2 sin 2 θ ) + 3 sin θ = 3 ⟹ 4 sin 2 θ − 3 sin θ + 1 = 0 2\cos(2\theta) + 3\sin\theta = 3 \implies 2(1-2\sin^2\theta) + 3\sin\theta = 3 \implies 4\sin^2\theta - 3\sin\theta + 1 = 0 2 cos ( 2 θ ) + 3 sin θ = 3 ⟹ 2 ( 1 − 2 sin 2 θ ) + 3 sin θ = 3 ⟹ 4 sin 2 θ − 3 sin θ + 1 = 0 .
Wait, if the equation was 2 cos ( 2 θ ) + 3 sin θ = 1 2\cos(2\theta) + 3\sin\theta = 1 2 cos ( 2 θ ) + 3 sin θ = 1 : 4 sin 2 θ − 3 sin θ − 1 = 0 ⟹ ( 4 sin θ + 1 ) ( sin θ − 1 ) = 0 4\sin^2\theta - 3\sin\theta - 1 = 0 \implies (4\sin\theta + 1)(\sin\theta - 1) = 0 4 sin 2 θ − 3 sin θ − 1 = 0 ⟹ ( 4 sin θ + 1 ) ( sin θ − 1 ) = 0 .
For the provided equation 2 cos ( 2 θ ) + 3 sin θ = 3 2\cos(2\theta) + 3\sin\theta = 3 2 cos ( 2 θ ) + 3 sin θ = 3 , there are no real solutions.
Answer: No solution.
sin 3 θ = sin ( 2 θ + θ ) = sin 2 θ cos θ + cos 2 θ sin θ \sin 3\theta = \sin(2\theta + \theta) = \sin 2\theta \cos \theta + \cos 2\theta \sin \theta sin 3 θ = sin ( 2 θ + θ ) = sin 2 θ cos θ + cos 2 θ sin θ
= ( 2 sin θ cos θ ) cos θ + ( 1 − 2 sin 2 θ ) sin θ = (2\sin\theta \cos\theta)\cos\theta + (1 - 2\sin^2\theta)\sin\theta = ( 2 sin θ cos θ ) cos θ + ( 1 − 2 sin 2 θ ) sin θ
= 2 sin θ ( 1 − sin 2 θ ) + sin θ − 2 sin 3 θ = 2\sin\theta(1 - \sin^2\theta) + \sin\theta - 2\sin^3\theta = 2 sin θ ( 1 − sin 2 θ ) + sin θ − 2 sin 3 θ
= 2 sin θ − 2 sin 3 θ + sin θ − 2 sin 3 θ = 3 sin θ − 4 sin 3 θ = 2\sin\theta - 2\sin^3\theta + \sin\theta - 2\sin^3\theta = 3\sin\theta - 4\sin^3\theta = 2 sin θ − 2 sin 3 θ + sin θ − 2 sin 3 θ = 3 sin θ − 4 sin 3 θ
sin 3 θ sin θ = 3 − 4 sin 2 θ \frac{\sin 3\theta}{\sin \theta} = 3 - 4\sin^2\theta s i n θ s i n 3 θ = 3 − 4 sin 2 θ . (QED)
cos A = 4 / 5 , sin A = 3 / 5 \cos A = 4/5, \sin A = 3/5 cos A = 4/5 , sin A = 3/5 (since acute). cos B = 12 / 13 , sin B = 5 / 13 \cos B = 12/13, \sin B = 5/13 cos B = 12/13 , sin B = 5/13 .
cos ( A + B ) = cos A cos B − sin A sin B = ( 4 / 5 ) ( 12 / 13 ) − ( 3 / 5 ) ( 5 / 13 ) = ( 48 − 15 ) / 65 = 33 / 65 \cos(A+B) = \cos A \cos B - \sin A \sin B = (4/5)(12/13) - (3/5)(5/13) = (48 - 15)/65 = 33/65 cos ( A + B ) = cos A cos B − sin A sin B = ( 4/5 ) ( 12/13 ) − ( 3/5 ) ( 5/13 ) = ( 48 − 15 ) /65 = 33/65 .
2 sin x cos x − cos x = 0 ⟹ cos x ( 2 sin x − 1 ) = 0 2\sin x \cos x - \cos x = 0 \implies \cos x(2\sin x - 1) = 0 2 sin x cos x − cos x = 0 ⟹ cos x ( 2 sin x − 1 ) = 0 .
cos x = 0 ⟹ x = π / 2 , 3 π / 2 \cos x = 0 \implies x = \pi/2, 3\pi/2 cos x = 0 ⟹ x = π /2 , 3 π /2 .
sin x = 1 / 2 ⟹ x = π / 6 , 5 π / 6 \sin x = 1/2 \implies x = \pi/6, 5\pi/6 sin x = 1/2 ⟹ x = π /6 , 5 π /6 .
Answer: π / 6 , π / 2 , 5 π / 6 , 3 π / 2 \pi/6, \pi/2, 5\pi/6, 3\pi/2 π /6 , π /2 , 5 π /6 , 3 π /2 .
sin ( 45 − 30 ) = sin 45 cos 30 − cos 45 sin 30 = 2 2 ⋅ 3 2 − 2 2 ⋅ 1 2 = 6 − 2 4 \sin(45-30) = \sin 45 \cos 30 - \cos 45 \sin 30 = \frac{\sqrt{2}}{2} \cdot \frac{\sqrt{3}}{2} - \frac{\sqrt{2}}{2} \cdot \frac{1}{2} = \frac{\sqrt{6}-\sqrt{2}}{4} sin ( 45 − 30 ) = sin 45 cos 30 − cos 45 sin 30 = 2 2 ⋅ 2 3 − 2 2 ⋅ 2 1 = 4 6 − 2 .
3 θ − π / 4 = π / 4 + k π ⟹ 3 θ = π / 2 + k π ⟹ θ = π / 6 + k π / 3 3\theta - \pi/4 = \pi/4 + k\pi \implies 3\theta = \pi/2 + k\pi \implies \theta = \pi/6 + k\pi/3 3 θ − π /4 = π /4 + k π ⟹ 3 θ = π /2 + k π ⟹ θ = π /6 + k π /3 .
1 − tan 2 θ 1 + tan 2 θ = 1 − sin 2 θ cos 2 θ 1 + sin 2 θ cos 2 θ = cos 2 θ − sin 2 θ cos 2 θ + sin 2 θ = cos 2 θ 1 = cos 2 θ \frac{1 - \tan^2\theta}{1 + \tan^2\theta} = \frac{1 - \frac{\sin^2\theta}{\cos^2\theta}}{1 + \frac{\sin^2\theta}{\cos^2\theta}} = \frac{\cos^2\theta - \sin^2\theta}{\cos^2\theta + \sin^2\theta} = \frac{\cos 2\theta}{1} = \cos 2\theta 1 + t a n 2 θ 1 − t a n 2 θ = 1 + c o s 2 θ s i n 2 θ 1 − c o s 2 θ s i n 2 θ = c o s 2 θ + s i n 2 θ c o s 2 θ − s i n 2 θ = 1 c o s 2 θ = cos 2 θ . (QED)
Direction vector d = B − A = ( 3 , − 3 , 2 ) \mathbf{d} = B - A = (3, -3, 2) d = B − A = ( 3 , − 3 , 2 ) .
r = ( 1 , 2 , 3 ) + λ ( 3 , − 3 , 2 ) \mathbf{r} = (1, 2, 3) + \lambda(3, -3, 2) r = ( 1 , 2 , 3 ) + λ ( 3 , − 3 , 2 ) .
d = ( 2 , − 1 , 2 ) , n = ( 1 , 2 , 2 ) \mathbf{d} = (2, -1, 2), \mathbf{n} = (1, 2, 2) d = ( 2 , − 1 , 2 ) , n = ( 1 , 2 , 2 ) .
sin θ = ∣ ( 2 ) ( 1 ) + ( − 1 ) ( 2 ) + ( 2 ) ( 2 ) ∣ 4 + 1 + 4 1 + 4 + 4 = ∣ 2 − 2 + 4 ∣ 3 ⋅ 3 = 4 / 9 \sin \theta = \frac{|(2)(1) + (-1)(2) + (2)(2)|}{\sqrt{4+1+4}\sqrt{1+4+4}} = \frac{|2-2+4|}{3 \cdot 3} = 4/9 sin θ = 4 + 1 + 4 1 + 4 + 4 ∣ ( 2 ) ( 1 ) + ( − 1 ) ( 2 ) + ( 2 ) ( 2 ) ∣ = 3 ⋅ 3 ∣2 − 2 + 4∣ = 4/9 .
θ = arcsin ( 4 / 9 ) ≈ 26.4 ∘ \theta = \arcsin(4/9) \approx 26.4^\circ θ = arcsin ( 4/9 ) ≈ 26. 4 ∘ .
P Q ⃗ = ( − 1 , 3 , − 1 ) , P R ⃗ = ( − 2 , 1 , 1 ) \vec{PQ} = (-1, 3, -1), \vec{PR} = (-2, 1, 1) P Q = ( − 1 , 3 , − 1 ) , P R = ( − 2 , 1 , 1 ) .
n = P Q ⃗ × P R ⃗ = ∣ i j k − 1 3 − 1 − 2 1 1 ∣ = ( 3 + 1 ) i − ( − 1 − 2 ) j + ( − 1 + 6 ) k = ( 4 , 3 , 5 ) \mathbf{n} = \vec{PQ} \times \vec{PR} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ -1 & 3 & -1 \\ -2 & 1 & 1 \end{vmatrix} = (3+1)\mathbf{i} - (-1-2)\mathbf{j} + (-1+6)\mathbf{k} = (4, 3, 5) n = P Q × P R = i − 1 − 2 j 3 1 k − 1 1 = ( 3 + 1 ) i − ( − 1 − 2 ) j + ( − 1 + 6 ) k = ( 4 , 3 , 5 ) .
Eq: 4 ( x − 2 ) + 3 ( y − 0 ) + 5 ( z − 1 ) = 0 ⟹ 4 x + 3 y + 5 z = 13 4(x-2) + 3(y-0) + 5(z-1) = 0 \implies 4x + 3y + 5z = 13 4 ( x − 2 ) + 3 ( y − 0 ) + 5 ( z − 1 ) = 0 ⟹ 4 x + 3 y + 5 z = 13 .
D = ∣ 2 ( 1 ) − 1 ( 1 ) + 2 ( 1 ) − 6 ∣ 4 + 1 + 4 = ∣ 2 − 1 + 2 − 6 ∣ 3 = ∣ − 3 ∣ 3 = 1 D = \frac{|2(1) - 1(1) + 2(1) - 6|}{\sqrt{4+1+4}} = \frac{|2-1+2-6|}{3} = \frac{|-3|}{3} = 1 D = 4 + 1 + 4 ∣2 ( 1 ) − 1 ( 1 ) + 2 ( 1 ) − 6∣ = 3 ∣2 − 1 + 2 − 6∣ = 3 ∣ − 3∣ = 1 .
d 1 = ( 2 , 1 , 1 ) , d 2 = ( 1 , − 1 , 0 ) \mathbf{d_1} = (2, 1, 1), \mathbf{d_2} = (1, -1, 0) d 1 = ( 2 , 1 , 1 ) , d 2 = ( 1 , − 1 , 0 ) . P 1 P 2 ⃗ = ( − 1 , 2 , 2 ) \vec{P_1P_2} = (-1, 2, 2) P 1 P 2 = ( − 1 , 2 , 2 ) .
Scalar triple product: ∣ − 1 2 2 2 1 1 1 − 1 0 ∣ = − 1 ( 1 ) − 2 ( − 1 ) + 2 ( − 2 − 1 ) = − 1 + 2 − 6 = − 5 ≠ 0 \begin{vmatrix} -1 & 2 & 2 \\ 2 & 1 & 1 \\ 1 & -1 & 0 \end{vmatrix} = -1(1) - 2(-1) + 2(-2-1) = -1 + 2 - 6 = -5 \neq 0 − 1 2 1 2 1 − 1 2 1 0 = − 1 ( 1 ) − 2 ( − 1 ) + 2 ( − 2 − 1 ) = − 1 + 2 − 6 = − 5 = 0 .
Answer: Not coplanar (Skew).
n 1 = ( 2 , − 1 , 1 ) , n 2 = ( 1 , 1 , − 2 ) \mathbf{n_1} = (2, -1, 1), \mathbf{n_2} = (1, 1, -2) n 1 = ( 2 , − 1 , 1 ) , n 2 = ( 1 , 1 , − 2 ) .
cos θ = ∣ 2 − 1 − 2 ∣ 6 6 = ∣ − 1 ∣ 6 = 1 / 6 \cos \theta = \frac{|2-1-2|}{\sqrt{6}\sqrt{6}} = \frac{|-1|}{6} = 1/6 cos θ = 6 6 ∣2 − 1 − 2∣ = 6 ∣ − 1∣ = 1/6 .
θ = arccos ( 1 / 6 ) ≈ 80.4 ∘ \theta = \arccos(1/6) \approx 80.4^\circ θ = arccos ( 1/6 ) ≈ 80. 4 ∘ .
L : r = ( 1 + 2 λ , − 2 + 3 λ , 3 − λ ) L: \mathbf{r} = (1+2\lambda, -2+3\lambda, 3-\lambda) L : r = ( 1 + 2 λ , − 2 + 3 λ , 3 − λ ) .
O P ⃗ ⋅ d = 0 ⟹ ( 1 + 2 λ ) ( 2 ) + ( − 2 + 3 λ ) ( 3 ) + ( 3 − λ ) ( − 1 ) = 0 \vec{OP} \cdot \mathbf{d} = 0 \implies (1+2\lambda)(2) + (-2+3\lambda)(3) + (3-\lambda)(-1) = 0 O P ⋅ d = 0 ⟹ ( 1 + 2 λ ) ( 2 ) + ( − 2 + 3 λ ) ( 3 ) + ( 3 − λ ) ( − 1 ) = 0
2 + 4 λ − 6 + 9 λ − 3 + λ = 0 ⟹ 14 λ = 7 ⟹ λ = 0.5 2 + 4\lambda - 6 + 9\lambda - 3 + \lambda = 0 \implies 14\lambda = 7 \implies \lambda = 0.5 2 + 4 λ − 6 + 9 λ − 3 + λ = 0 ⟹ 14 λ = 7 ⟹ λ = 0.5 .
Point: ( 1 + 1 , − 2 + 1.5 , 3 − 0.5 ) = ( 2 , − 0.5 , 2.5 ) (1+1, -2+1.5, 3-0.5) = (2, -0.5, 2.5) ( 1 + 1 , − 2 + 1.5 , 3 − 0.5 ) = ( 2 , − 0.5 , 2.5 ) .
sin C = 1 − ( 1 / 4 ) 2 = 15 / 4 \sin C = \sqrt{1 - (1/4)^2} = \sqrt{15}/4 sin C = 1 − ( 1/4 ) 2 = 15 /4 .
Area = 1 2 a b sin C = 1 2 ( 7 ) ( 8 ) 15 4 = 7 15 ≈ 27.1 = \frac{1}{2}ab \sin C = \frac{1}{2}(7)(8)\frac{\sqrt{15}}{4} = 7\sqrt{15} \approx 27.1 = 2 1 ab sin C = 2 1 ( 7 ) ( 8 ) 4 15 = 7 15 ≈ 27.1 .
∠ R = 180 − ( 45 + 60 ) = 75 ∘ \angle R = 180 - (45+60) = 75^\circ ∠ R = 180 − ( 45 + 60 ) = 7 5 ∘ .
P R sin 60 = 10 sin 75 ⟹ P R = 10 ⋅ 3 2 sin 75 ≈ 8.66 0.966 ≈ 8.96 cm \frac{PR}{\sin 60} = \frac{10}{\sin 75} \implies PR = \frac{10 \cdot \frac{\sqrt{3}}{2}}{\sin 75} \approx \frac{8.66}{0.966} \approx 8.96\text{ cm} s i n 60 P R = s i n 75 10 ⟹ P R = s i n 75 10 ⋅ 2 3 ≈ 0.966 8.66 ≈ 8.96 cm .
tan ( A + B ) = tan ( 180 − C ) = − tan C \tan(A+B) = \tan(180-C) = -\tan C tan ( A + B ) = tan ( 180 − C ) = − tan C .
tan A + tan B 1 − tan A tan B = − tan C ⟹ tan A + tan B = − tan C + tan A tan B tan C \frac{\tan A + \tan B}{1 - \tan A \tan B} = -\tan C \implies \tan A + \tan B = -\tan C + \tan A \tan B \tan C 1 − t a n A t a n B t a n A + t a n B = − tan C ⟹ tan A + tan B = − tan C + tan A tan B tan C .
tan A + tan B + tan C = tan A tan B tan C \tan A + \tan B + \tan C = \tan A \tan B \tan C tan A + tan B + tan C = tan A tan B tan C . (QED)
r = 10 sin α , h = 10 cos α r = 10 \sin \alpha, h = 10 \cos \alpha r = 10 sin α , h = 10 cos α .
V = 1 3 π r 2 h = 1 3 π ( 100 sin 2 α ) ( 10 cos α ) = 1000 3 π sin 2 α cos α V = \frac{1}{3}\pi r^2 h = \frac{1}{3}\pi (100 \sin^2 \alpha)(10 \cos \alpha) = \frac{1000}{3}\pi \sin^2 \alpha \cos \alpha V = 3 1 π r 2 h = 3 1 π ( 100 sin 2 α ) ( 10 cos α ) = 3 1000 π sin 2 α cos α .
2 sin ( θ + π / 6 ) = 1 ⟹ sin ( θ + π / 6 ) = 1 / 2 2\sin(\theta + \pi/6) = 1 \implies \sin(\theta + \pi/6) = 1/2 2 sin ( θ + π /6 ) = 1 ⟹ sin ( θ + π /6 ) = 1/2 .
θ + π / 6 = π / 6 , 5 π / 6 ⟹ θ = 0 , 2 π / 3 \theta + \pi/6 = \pi/6, 5\pi/6 \implies \theta = 0, 2\pi/3 θ + π /6 = π /6 , 5 π /6 ⟹ θ = 0 , 2 π /3 .
Check range: 0 , 2 π / 3 0, 2\pi/3 0 , 2 π /3 . (Also 2 π 2\pi 2 π is equivalent to 0 0 0 ).
n = ( 2 , 3 , − 1 ) \mathbf{n} = (2, 3, -1) n = ( 2 , 3 , − 1 ) . Plane: 2 ( x − 1 ) + 3 ( y − 1 ) − 1 ( z − 1 ) = 0 ⟹ 2 x + 3 y − z = 4 2(x-1) + 3(y-1) - 1(z-1) = 0 \implies 2x + 3y - z = 4 2 ( x − 1 ) + 3 ( y − 1 ) − 1 ( z − 1 ) = 0 ⟹ 2 x + 3 y − z = 4 .
Dist = ∣ − 4 ∣ 4 + 9 + 1 = 4 14 ≈ 1.07 = \frac{|-4|}{\sqrt{4+9+1}} = \frac{4}{\sqrt{14}} \approx 1.07 = 4 + 9 + 1 ∣ − 4∣ = 14 4 ≈ 1.07 .