To find the value of sine of 49.5 0r 54.6, we have to either use calculator or trigonometric table.
However, you can use approximation to find a value close to sin 49.5 or cos 54.6
sine 49.5 is approximately half way between sin 45 and sine 54.
So find the values of sin 45 and sin 54 and find the average.
It gives apprximate value of sin 49.5
Similarly cos 54.6 will be approximately equal to cos 54.
The value of cos 54 can be found using trigonometric ratios.
So when trigonometric ratios are not helpful to find value of any angle,
we can take help of approximation as shown above.