Question

3sina-4sin4a/sin5a if a=-45 degree

Answer 1

Given:

The given expression is:

$\dfrac{3\sin a-4\sin 4a}{\sin 5a}$

To find:

The value of the given expression at $a=-45$.

Solution:

We have,

$\dfrac{3\sin a-4\sin 4a}{\sin 5a}$

Substituting $a=-45$, we get

$\dfrac{3\sin (-45)-4\sin [4(-45)]}{\sin [5(-45)]}$

$=\dfrac{-3\sin (45)+4\sin (180)}{-\sin (225)}$

$=\dfrac{-3\sin (45)+4\sin (180)}{-\sin (180+45)}$

$=\dfrac{-3\sin (45)+4\sin (180)}{\sin (45)}$

On substituting $\sin (180)$, we get,

$=\dfrac{-3\sin (45)+4(0)}{\sin (45)}$

$=\dfrac{-3\sin (45)+0}{\sin (45)}$

$=\dfrac{-3\sin (45)}{\sin (45)}$

$=-3$

Therefore, the value of the given expression at  $a=-45$ is $-3$.