Find the value of cos(20) using double-angle formula given:

20 points ! i need asap

the correct answer is -1/9

explanation

cos(2A)

=cos(A+A)

=cosA.cosA - sinA.sinA

=cos ^2A- sin^2A

=cos^2A - 1 + cos^2A

=2cos^2A-1

putting the value of cos A -2/3

2*(-2/3)^2-1

=2*4/9-1

=8/9-1

=-1/9

here is put theta as A because I don't find theta symbol

don't forget to mark as brainllest answer

for the friend request.

when a figure, such as triangle (xyz) is reflected over the line y = x to create x'y'z' the x-coordinates and y-coordinates of the original image (pre-image) will be reversed for the image. (e.g., (x, y) > (y, x)) this means that the pre-image position of the x- and y-coordinates switch places which in turn provides a mirror like image of the original xyz.  

i notice that when i draw a line segment from x to x', that the points are parallel from each other -- they are exactly across from each other and do not intersect with any other points.  

yes, think i would see the same characteristic if you drew the line segment connecting y with the reflecting line and then y' with the reflecting line because of the essence of reflections. because it is a mirror image, each point was effected the same way which leads me to conclude that they same would apply to y and y'.

step-by-step explanation: