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Bumek [7]
3 years ago
6

20 POINTS!!!

Mathematics
2 answers:
elena-s [515]3 years ago
8 0

\ \ \dfrac{2}{\sqrt{3} \cos (x) + \sin(x)} = \sec\left(\frac{\pi}{6} - x\right)

Right-hand side

\text{RHS} = \sec\left(\dfrac{\pi}{6} - x\right)

Since \sec x = \frac{1}{\cos x}, it follows that

\sec\left(\frac{\pi}{6} - x\right) = \dfrac{1}{\cos\left(\frac{\pi}{6} - x\right) }

So we can rewrite

\begin{aligned} \text{RHS} &= \sec\left(\dfrac{\pi}{6} - x\right) \\ &= \dfrac{1}{\cos\left(\frac{\pi}{6} - x\right)} \end{aligned}

We have a cosine difference identity for the denominator:

\begin{aligned} \cos(A-B) &= \cos A \cos B + \sin A \sin B \\ \cos\left(\tfrac{\pi}{6} - x\right) &= \cos\left(\tfrac{\pi}{6}\right) \cos (x) + \sin\left(\tfrac{\pi}{6}\right)\sin(x) \end{aligned}

Since \sin\left(\tfrac{\pi}{6}\right) = 1/2 and \cos\left(\tfrac{\pi}{6}\right) = \sqrt{3}/2, we have

\begin{aligned}\cos\left(\tfrac{\pi}{6} - x\right) &= \cos\left(\tfrac{\pi}{6}\right) \cos (x) + \sin\left(\tfrac{\pi}{6}\right)\sin(x) \\ &= \tfrac{\sqrt{3}}{2}\cos (x) + \tfrac{1}{2}\sin(x) \end{aligned}

Using this in the right-hand side

\begin{aligned} \text{RHS} &= \dfrac{1}{\cos\left(\frac{\pi}{6} + x\right)} \\ &= \frac{1}{\tfrac{\sqrt{3}}{2}\cos (x) + \tfrac{1}{2}\sin(x)} \end{aligned}

Notice how we have tiny denominators of 2.If we multiply the numerator and denominator of the entire fraction, we will deal with those twos, as 2 will distribute and cancel.

\begin{aligned} \text{RHS} &= \frac{1}{\tfrac{\sqrt{3}}{2}\cos (x) + \tfrac{1}{2}\sin(x)} \\ &=\frac{2 \cdot(1)}{2 \cdot \left(\tfrac{\sqrt{3}}{2}\cos (x) + \tfrac{1}{2}\sin(x)\right)} \\ &= \frac{2}{\sqrt{3} \cos (x) + \sin(x)} \\ &= \text{LHS} \end{aligned}

notka56 [123]3 years ago
6 0

\dfrac{2}{\sqrt3\cos x+\sin x}=\sec\left(\dfrac{\pi}{6}-x\right)\\\\\dfrac{2}{\sqrt3\cos x+\sin x}=\dfrac{1}{\cos\left(\dfrac{\pi}{6}-x\right)}\ \ \ \ \ (*)\\----------------\\\\\cos\left(\dfrac{\pi}{6}-x\right)\ \ \ \ |\text{use}\ \cos(x-y)=\cos x\cos y+\sin x\sin y\\\\=\cos\dfrac{\pi}{6}\cos x+\sin\dfrac{\pi}{6}\sin x=\dfrac{\sqrt3}{2}\cos x+\dfrac{1}{2}\sin x=\dfrac{\sqrt3\cos x+\sin x}{2}\\------------------------------

(*)\\R_s=\sec\left(\dfrac{\pi}{6}-x\right)=\dfrac{1}{\cos\left(\dfrac{\pi}{6}-x\right)}=\dfrac{1}{\dfrac{\sqrt3\cos x+\sin x}{2}}\\\\=\dfrac{2}{\sqrt3\cos x+\sin x}=L_s

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