Can anyone tell me at what point the line y=cos(x) is zero? The only thing that I've got to calculate it with is a calculator which I suspect isn't being too precise about it's values.

y=cos(x) right at this.............................................. .................................................. .................................................. .............................. .................................................. ........................point. How could you not know that? Must be those redneck Denmark schools [img]tongue.gif[/img] Sorry Nob [img]smile.gif[/img]

90 ;)

Excellent. Thanks for the aid, LS.

90,270,450,630,810,990 ...... you kinda get the idea ..... [img]smile.gif[/img]

.5 pi, 1.5pi and every rotation thereof.

Or havent you done radians yet?

For what its worth, calculators are precice at the zero points of a trig function. But only then.

.5 pi, 1.5pi and every rotation thereof.

Or havent you done radians yet?

For what its worth, calculators are precice at the zero points of a trig function. But only then.</font>[/QUOTE]I've done radians, hmm i wonder why i couldnt give the answer in radians .....

<font color = lightgreen>whacky and andrewas are completely correct. cos(x) = 0 for x = ((2k + 1)/2) * pi, where k is any integer value and x is a radian measure.

Calculators are funny. You can enter any number for a degree measure and it will give you the cosine of that number; however, if you enter any number in between -1 and 1 you will get the inverse cosine only for degrees between -90 and +90 degrees.</font>

the term "any integer" implies this, but remember that k can be negative as well.

e.g. -pi/2, -3pi/2 , ....

<font color="lightblue">If you`re working in degrees, it`s just the sine curve outset by 90. [img]smile.gif[/img]

So for a single revolution, if sin(0)=0, 180, 360
Then, cos(90) = 0, 180, 360

If cos(0)= 90, 270
Then sin (90)= 90, 270

If you know one, you know the other- the sine of an angle is equal to the cosine of a complimentary angle. [img]smile.gif[/img] </font>