That is the definition. If you take your unit circle (a circle with radius 1 centered at the origin (0,0). you start at (1,0) and go counterclockwise around the circle 90° you end up at (0,1) that 0 is the cosine of the angle 90°
In fact, you don't even need the unit circle. Take a circle of any radius r, and draw a ray at 90 degrees. This will intersect the y-axis. So as above, the coordinates are (0,r) (instead of (0,1)) so cos(90 degrees)=x/r=0/r=0
Cosine (0) = 1 Sin(0) = 0 The sine and cosine curves are two intertwining curves, that complement each other, hence the words 'Sine (Curve) and Cosine ( COmplementary Curve).
The Y-Intercept of the cosine function is X = 0, Y = cosine(0) = 1.
sin(30) = sin(90 - 60) = sin(90)*cos(60) - cos(90)*sin(60) = 1*cos(60) - 0*sin(60) = cos(60).
Cos(0) = 1
The cofunction identity for cosine states that the cosine of an angle is equal to the sine of its complement. Specifically, this can be expressed as (\cos(t) = \sin\left(\frac{\pi}{2} - t\right)) in radians or (\cos(t) = \sin(90^\circ - t)) in degrees. This relationship highlights the complementary nature of the sine and cosine functions.
Cosine of -90 is 0.
The Unit Circle is a circle that has a radius of 1 and a center at the origin. If you look at the unit circle 90 degrees is at the point (0,1). Cosine is equal to the x value of a point on the Unit Circle. The line created to the point (0,1) on the unit circle when the degree is 90 is completely vertical, which in turn makes the x value 0 and thus, cosine of 90 = 0. Read more >> Options >> http://www.answers.com?initiator=FFANS
The cosine of 90 degrees is zero.
Cosine (0) = 1 Sin(0) = 0 The sine and cosine curves are two intertwining curves, that complement each other, hence the words 'Sine (Curve) and Cosine ( COmplementary Curve).
The law of cosines with a right angle is just the pythagorean theorem. The cosine of 90 degrees is 0. That is why the hypotenuse squared is equal to the sum of both of the legs squared
Just like the sine function displaced by pi/2. In other words the cosine equals 1 at 0 degrees, 0 at 90 degrees, -1 at 180 and so on.
Cosine of 90 degrees is zero.
If the numerator is 0 AND the denominator is not 0, then the ratio is 0. And cosine of 0 is 1.
Zero
The Y-Intercept of the cosine function is X = 0, Y = cosine(0) = 1.
Because it tends to infinity. Additionally, tangent can be expressed as sin theta divided by cos theta. The sine of 90 is 1. The cosine of 90 is 0. That would be 1 divided by 0, or division by zero; which is undefined.
Secant is 1 over cosine and cosine 0 equals 1.