Ans: Given: 
We know that 
While comparing the angles of sin, we get
![\[\Rightarrow \varphi=30^{\circ}\]](https://www.learnatnoon.com/s/wp-content/ql-cache/quicklatex.com-125762f37afa00bad56d2689a1461bec_l3.png "Rendered by QuickLaTeX.com")
Class vill Mathematics
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Substitute 
![\[\begin{array}{l} 3 \cos \varphi-4 \cos ^{3} \varphi=3 \cos \left(30^{\circ}\right)-4 \cos ^{3}\left(30^{\circ}\right) \\ \Rightarrow 3\left(\frac{\sqrt{3}}{2}\right)-4\left(\frac{3 \sqrt{3}}{8}\right) \Rightarrow 0 \end{array}\]](https://www.learnatnoon.com/s/wp-content/ql-cache/quicklatex.com-6b0f0c75713c61f55d5d0c1a0610ea0e_l3.png "Rendered by QuickLaTeX.com")
Therefore, 
Hence proved.
If
Ans: Given:
We know that
While comparing the angles of sin, we get
Class vill Mathematics
whw vedantu.com
1
Substitute
Therefore,
Hence proved.