Now, look at the pics again
Now, the sum of all angle in a triangle is 180°. The angle in front of the tilted side is a right angle. So it took 90° all by it self. That left only 90° of angle to be divided between x and y.
Hence, x+y=90°.
That means
y=90°-x
Naturally
sin(x)=cos(90°-x)
cos(x)=sin(90°-x)
The same way but less importantly
sec(x)=cosec(y)=cosec(90°-x)
cosec(x)=sec(y)=sec(90°-x)
There you go. Your first few formulas. All those are so easy if you can just derive them. NEVER memorize formulas. That is more dangerous than the violent or steamy video games. The latter are not dangerous at all. Oh ya, always be suspicious of what teachers told you. Your parents will thank me for this.
Incoming search terms:
- sin(90-theta) (28)
- cos 90-theta (27)
- cos(90-theta) (25)
- cos(90 theta) (24)
- sin 90-theta (23)
- cos 90 theta (16)
- sin 90 theta (15)
- sine 90 theta (13)
- cos 90 - theta (8)
- sin(90 theta) (8)