Home › ACSEE (Form 6) › Advanced Mathematics › Trigonometry › Expressed in the form $R\sin(x-\beta)$, the expr…
Expressed in the form $R\sin(x-\beta)$, the expression $3\sin x-2\cos x$ has:
A$R=\sqrt{13}$, $\beta=33.69^{\circ}$
B$R=5$, $\beta=33.69^{\circ}$
C$R=\sqrt{13}$, $\beta=56.31^{\circ}$
D$R=\sqrt5$, $\beta=33.69^{\circ}$
Answer & Solution
Correct answer: A. $R=\sqrt{13}$, $\beta=33.69^{\circ}$
1. Expand the target form: $R\sin(x-\beta)=R\sin x\cos\beta-R\cos x\sin\beta$.
2. Match coefficients: $R\cos\beta=3$ and $R\sin\beta=2$.
3. Squaring and adding: $R^2=3^2+2^2=13$, so $R=\sqrt{13}$.
4. Dividing: $\tan\beta=\dfrac23$, so $\beta=33.69^{\circ}$.
5. $R=5$ adds the coefficients instead of their squares; $56.31^{\circ}$ inverts the tangent ratio.
_Source: NECTA ACSEE 2023 Advanced Mathematics 142/2, Question 5: Trigonometry_
Related questions
Given $ in x=\dfrac35$ with $x$ obtuse and $\cos y=\dfrac{24}{25}$ with $y$ acute, the exaGiven $\tan(2x+y)=2$ and $\tan 2x=\dfrac32$, the value of $\tan y$ is:Factorised using the factor formulae, $\cos\theta-\cos3\theta-\cos5\theta+\cos7\theta$ equValues of trigonometric functions at 0, 30, 45, 60 and 90 degrees are:The sine function is positive for angles between zero and:In the fourth quadrant, a is positive and b is:In the third quadrant, the coordinates a and b are:In the second quadrant, the coordinate a is: