+0

# how does?

0
201
4

-3cos^2(π/2)

Guest Jan 1, 2015

#4
+91509
+10

-3cos²(-π/2)=0    also

I would like to try and explain something to you.

http://www.mathsisfun.com/sine-cosine-tangent.html

There is an interactive unit circle at the bottom of the page.  You can choose radians or degrees.

Now the hypotenuse of the triangels is the radius of the cirlcle which is 1

The sine of the angle is given by the y value on the circumference of the unit circle

The cos of the angle is given by the x value on the circumference of the unit circle.

The tan of the angle is given by the y value over the x value on the circumference of the unit circle.

Play with it and really try to understand the concept.  It will help you enormously if you really understand this.

At pi/2 and at -pi/2 the x value is 0 so cos of these angles will be zero!

Sine will be 1 and -1 respectively.  Tan will be undfined - you cannot divide by 0  :)

Melody  Jan 2, 2015
Sort:

#1
+17711
+10

cos(π/2) = 0   --->   cos²(π/2) = 0   --->   -3cos²(π/2) = 0

geno3141  Jan 1, 2015
#2
0

but if it were -π/2 ? plz

Guest Jan 1, 2015
#3
0

sorry -π/4 ?

Guest Jan 1, 2015
#4
+91509
+10

-3cos²(-π/2)=0    also

I would like to try and explain something to you.

http://www.mathsisfun.com/sine-cosine-tangent.html

There is an interactive unit circle at the bottom of the page.  You can choose radians or degrees.

Now the hypotenuse of the triangels is the radius of the cirlcle which is 1

The sine of the angle is given by the y value on the circumference of the unit circle

The cos of the angle is given by the x value on the circumference of the unit circle.

The tan of the angle is given by the y value over the x value on the circumference of the unit circle.

Play with it and really try to understand the concept.  It will help you enormously if you really understand this.

At pi/2 and at -pi/2 the x value is 0 so cos of these angles will be zero!

Sine will be 1 and -1 respectively.  Tan will be undfined - you cannot divide by 0  :)

Melody  Jan 2, 2015

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