====== Question 4, Review Exercise ======
Solutions of Question 4 of Review Exercise of Unit 08: Fundamental of Trigonometry. This is unit of Model Textbook of Mathematics for Class XI published by National Book Foundation (NBF) as Federal Textbook Board, Islamabad, Pakistan. 

=====Question 4(i)=====
Find the values of: $\dfrac{1+\tan 15^{\circ}}{1-\tan 15^{\circ}}$

** Solution. **

\begin{align*}
&\frac{1+\tan 15^{\circ}}{1-\tan 15^{\circ}}\\
=&\frac{1+\tan 15^{\circ}}{1-1 \cdot \tan 15^{\circ}}\\
=&\frac{\tan 45^{\circ} + \tan 15^{\circ}}{1 - \tan 45^{\circ} \tan 15^{\circ}}\\
=& \tan(45^{\circ} + 15^{\circ})\\
=& \tan(60^{\circ})\\
=&1.732
\end{align*}

=====Question 4(ii)=====
Find the values of: $\cos 70^{\circ} \cdot \cos 20^{\circ}-\sin 70^{\circ} \sin 20^{\circ}$

** Solution. **

\begin{align*}
&\cos 70^{\circ} \cdot \cos 20^{\circ} - \sin 70^{\circ} \sin 20^{\circ} \\
=& \cos(70^{\circ} + 20^{\circ}) \\
=& \cos(90^{\circ}) \\
=& 0
\end{align*}






====Go to ====

<text align="left"><btn type="primary">[[math-11-nbf:sol:unit08:Re-ex-p3|< Question 3]]</btn></text>
<text align="right"><btn type="success">[[math-11-nbf:sol:unit08:Re-ex-p5|Question 5 & 6 >]]</btn></text>