2016年8月25日 · #cos(-pi)=-1# Explanation: Consider a definition of a function #cos(theta)# on a unit circle as an abscissa (X-coordinate) of a point that lies on this unit circle and an angle from the positive direction of the X-axis to a radius to this point counterclockwise equals to #theta# .

2016年9月30日 · Use the known trigonometric identity . #cos(a+b)=cosa*cosb-sina*sinb# we have that. #cos(x+pi/2)=cosx*cos(pi/2)-sinx*sin(pi/2)=cosx*0-sinx*1=-sinx#

What is the value of {eq}\cos \dfrac{\pi}{4} {/eq} ? Exact Values of Trigonometric Functions for Common Special Angles In a unit circle, we can find derived or exact values for special angles and trigonometric functions.

2018年7月3日 · #cos (pi/3) = cos 60^@ = 1/2#![https://www.quora.com /How-do-I-use-a-unit-circle-in-math]()

2015年2月4日 · Here is another way to solve this problem. It's known that #sin^2(phi)+cos^2(phi)=1# for any angle #phi#. ...

2016年5月1日 · This is a well used trig. relation along with #sin(pi/2-theta)#. that is : #cos(pi/2-theta)=sintheta" and " sin(pi/2-theta)=costheta#

2016年9月9日 · Use the trig identity: cos (a + b) = cos a.cos b - sin a.sin b #cos (pi + pi/3) = cos pi.cos (pi/3) - sin pi.sin (pi/3)#

2016年4月4日 · Let's first convert to degrees. The conversion ratio between degrees and radians is 180/pi. pi/4 xx 180/pi = 45^@ Now, we must think of the special triangle that contains a 45^@ angle. This would be the following triangle. The definition of cos is adjacent/hypotenuse. Therefore, our ratio is 1/sqrt(2). However, often, teachers want the denominator to be …

2016年10月3日 · How do you show that #(costheta)(sectheta) = 1# if #theta=pi/4#? See all questions in Trigonometric Functions of Any Angle Impact of this question

2015年9月5日 · How do you show that #(costheta)(sectheta) = 1# if #theta=pi/4#? See all questions in Trigonometric Functions of Any Angle Impact of this question