In this video, we will learn to find the value
cosine of -135 degree. As we know, the trigonometry identity cos(-x)
=cos(x). The video explaining how to derive this identity
is appearing in the upper right corner. Also the URL address of the video has been
mentioned in the description section. Let’s apply the above identity for cos(-135
degree). Here x is 135 degree. So, cos(-135 degree)=cos(135 degree). As, 135 degree is equal to 180 degree minus
45 degree. So, cos(-135) is equal to cos(180 – 45). As we know, the trigonometry identity cos(180
+ x)=-cos(x). The video explaining how to derive this identity
is appearing in the upper right corner. Also the URL address of the video has been
mentioned in the description section. Let’s apply the above identity for cos(180
– 45), Here x is 45 degree. So, cos(-135 degree)=-cos(45 degree). We know, the value of cos(45)=1/sqrt of
2 So, value of cos(-135)=-1/ sqrt of 2