cos(-225°) is coterminal with cos 135°
By the CAST rule, cos 135° = -cos 45°
= -1/√2 or -√2/2
Find the value of cos(-225).
4 answers
cos(-x) = cos(x)
cos(x-180) = -cos(x)
See if that helps you.
Or, draw the triangle in standard position, and recall that
cos(x) = x/r
cos(x-180) = -cos(x)
See if that helps you.
Or, draw the triangle in standard position, and recall that
cos(x) = x/r
Explain me in terms of unit circle.
Ok
Going either -225° or 135°, you would end up in the same position, right?
Now draw you 1 unit radius at 135 and sketch your right-angled triangle.
You have a right-angled triangle with a base and height of √2.
the value of x = -√2 and the the value of y is +√2
cos -225 = cos 135 = x/r = -√2/2
Going either -225° or 135°, you would end up in the same position, right?
Now draw you 1 unit radius at 135 and sketch your right-angled triangle.
You have a right-angled triangle with a base and height of √2.
the value of x = -√2 and the the value of y is +√2
cos -225 = cos 135 = x/r = -√2/2
1 answer