Given $sec\ \theta = \frac{13}{12}$, calculate all other trigonometric ratios.

AcademicMathematicsNCERTClass 10

Given:

\( \sec \theta=\frac{13}{12} \)

To do:

We have to find the values of the other trigonometric ratios.

Solution:  

We know that,

In a right-angled triangle $ABC$ with a right angle at $B$,

By Pythagoras theorem,

$AC^2=AB^2+BC^2$

By trigonometric ratios definitions,

$sin\ A=\frac{Opposite}{Hypotenuse}=\frac{BC}{AC}$

$cos\ A=\frac{Adjacent}{Hypotenuse}=\frac{AB}{AC}$

$tan\ A=\frac{Opposite}{Adjacent}=\frac{BC}{AB}$

$cosec\ A=\frac{Hypotenuse}{Opposite}=\frac{AC}{BC}$

$sec\ A=\frac{Hypotenuse}{Adjacent}=\frac{AC}{AB}$

$cot\ A=\frac{Adjacent}{Opposite}=\frac{AB}{BC}$

Here,

Let $sec\ \theta=\frac{AC}{AB}=\frac{13}{12}$

$AC^2=AB^2+BC^2$

$\Rightarrow (13)^2=(12)^2+(BC)^2$

$\Rightarrow BC^2=169-144$

$\Rightarrow BC=\sqrt{25}=5$

Therefore,

$sin\ \theta=\frac{BC}{AC}=\frac{5}{13}$

$cos\ \theta=\frac{AB}{AC}=\frac{12}{13}$

$tan\ \theta=\frac{BC}{AB}=\frac{5}{12}$

$cosec\ \theta=\frac{AC}{BC}=\frac{13}{5}$

$cot\ \theta=\frac{AB}{BC}=\frac{12}{5}$ 

raja
Updated on 10-Oct-2022 13:22:11

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