## Friday, December 27, 2013

### 76-Basics of Trigonometry - 04

Blog-76
Dear Students,
Now we will study the next part of trigonometry.

Today we will study trigonometric ratios of 0°, 30°, 45°, 60°.

1) Trigonometric ratios of an angle =  0°

Here angle AOP is of 0°.
According to the diagram, OP = r and the coordinates of point P are (r, 0). So x-coordinate of point P is r and the y-coordinate of point P is 0.

So, all the trigonometric ratios of 0° with
x = r,
y = 0,
r  = r.

 a) sin 0° = y/r     sin 0° = 0/r        sin 0° = 0 b) cos 0° = x/r     cos 0° = r/r        cos 0° = 1 c) tan 0° = y/x     tan 0° = 0/r        tan 0° = 0 d) csc 0° = r/y     csc 0° = r/0          csc 0° = ∞ e) sec 0° = r/x     sec 0° = r/r        sec 0° = 1 f) cot 0° = x/y     cot 0° = r/0        cot 0° = ∞

2) Trigonometric ratios of an angle 30°
Here angle AOP is of 30°.

We know that the side opposite to 30° is half the hypotenuse and side opposite to 60° is √3/ 2 times the hypotenuse.
So if hypotenuse OP = r, then  AP = r/2 and OA = (√3 r)/ 2.
Here the coordinates of point P will be P ((√3 r)/ 2, r/2).
So, all the trigonometric ratios of 30° with
x = (√3 r)/ 2,
y = r/2,
r = r.

 a) sin 30° = y/r     sin 30° = (r/2)/r        sin 30° = 1/2 b) cos 30° = x/r     cos 30° = [(√3 r)/2]/r            cos 30° = √3/2 c) tan 30° = y/x     tan 30° = (r/2)/(√3 r)/2        tan 30° = 1/√3 d) csc 30° = r/y     csc 30° =  r/(r/2)          csc 30° = 2 e) sec 30° = r/x     sec 30° = r/[(√3 r)/2]        sec 30° = 2/√3 f) cot 30° = x/y     cot 30° = [(√3 r)/ 2]/(r/2)        cot 30° = √3

3) Trigonometric ratios of an angle 45°
Here angle AOP is of 45°.

We know that the side opposite to 45° is 1/√2 times the hypotenuse.
So if hypotenuse OP = r, then  AP = r/√2 and OA = r/√2.
Here the coordinates of point P will be P (r/√2r/√2).
So, all the trigonometric ratios of 45° with
x = r/√2,
y = r/√2,
r = r.

 a) sin 45° = y/r      sin 45°  = [r/√2]/r         sin 45°  = 1/√2 b) cos 45° = x/r      cos 45° = [r/√2]/r      cos 45° = 1/√2 c) tan 45° = y/x      tan 45°  = [r/√2]/ [r/√2]        tan 45°  = 1 d) csc 45° = r/y     csc 45° =  r/[r/√2]     csc 45° = √2 e) sec 45° = r/x     sec 45° = r/[r/√2]        sec 45° = √2 f) cot 45° = x/y     cot 45° = [r/√2]/ [r/√2]        cot 45° = 1

4) Trigonometric ratios of an angle 60°
Here angle AOP is of 60°.

We know that the side opposite to 60° is √3/2 times the hypotenuse and side opposite to 30° is half times the hypotenuse.
So if hypotenuse OP = r, then  AP = (√3 r)/2 and OA = r/2.
Here the coordinates of point P will be P (r/2(√3 r)/2).
So, all the trigonometric ratios of 60° with
x = r/2,
y = (√3 r)/2,
r = r.

 a) sin 60° = y/r     sin 60° = [(√3 r)/2]/r        sin 60° = √3/2 b) cos 60° = x/r      cos 60° = [r/2]/r      cos 60° = 1/2 c) tan 60° = y/x     tan 60° = [(√3 r)/2]/[r/2]       tan 60° = √3 d) csc 60° = r/y     csc 60° =  r/[(√3 r)/2]     csc 60° = 2/√3 e) sec 60° = r/x     sec 60° = r/[r/2]        sec 60° = 2 f) cot 60° = x/y     cot 60° = [r/2]/[(√3 r)/2]        cot 60° = 1/√3

In the next blog, we will study the trigonometric ratios of 90°, 180° and the tabulated form of all the trigonometric ratios.

Anil Satpute