State whether the following are true or false. Justify your answer.
$(i)$ The value of tan $A$ is always less than $1 .$
$(ii)$ $\sec A=\frac{12}{5}$ for some value of angle $A$.
Consider a $\triangle ABC ,$ right-angled at $B$.
$\tan A=\frac{\text { Side opposite to } \angle A }{\text { Side adjacent to } \angle A }$
$=\frac{12}{5}$
But $\frac{12}{5}>1$
$\therefore \tan A>1$
So, tan $A<1$ is not always true.
Hence, the given statement is false.
$(ii)$ $\sec A=\frac{12}{5}$
$\frac{\text { Hypotenuse }}{\text { Side adjacent to } \angle A }=\frac{12}{5}$
$\frac{A C}{A B}=\frac{12}{5}$
Let $AC$ be $12 k , AB$ will be $5 k ,$ where $k$ is a positive integer.
Applying Pythagoras theorem in $\triangle ABC ,$ we obtain
$AC ^{2}= AB ^{2}+ BC ^{2}$
$(12 k)^{2}=(5 k)^{2}+ BC ^{2}$
$144 k^{2}=25 k^{2}+B C^{2}$
$BC ^{2}=119 k ^{2}$
$BC =10.9 k$
It can be observed that for given two sides $AC =12 k$ and $AB =5 k$,
BC should be such that,
$AC - AB < BC < AC + AB$
$12 k-5 k< BC <12 k+5 k$
$7 k< BC <17 k$
However, $BC =10.9 k$. Clearly, such a triangle is possible and hence, such value of $\sec A$ is Possible.
Hence,the given statement is false.
In a right triangle $A B C$, right-angled at $B$. if $\tan A =1,$ then verify that $2 \sin A \cos A=1$
Evaluate:
$\frac{\sin 18^{\circ}}{\cos 72^{\circ}}$
In $\triangle$ $PQR,$ right-angled at $Q$ (see $Fig.$), $PQ =3 \,cm$ and $PR =6 \,cm$. Determine $\angle QPR$ and $\angle PRQ$.
Evaluate the following:
$\frac{\cos 45^{\circ}}{\sec 30^{\circ}+\operatorname{cosec} 30^{\circ}}$
State whether the following are true or false. Justify your answer.
The value of $\cos \theta$ increases as $\theta$ increases