Tofind the value of cos Ο/4 using the unit circle: Rotate 'r' anticlockwise to form pi/4 angle with the positive x-axis. The cos of pi/4 equals the x-coordinate (0.7071) of the point of intersection (0.7071, 0.7071) of unit circle and r. Hence the value of cos pi/4 = x = 0.7071 (approx)
Explanation We know that ,cos is an even function. β cos( βΞΈ) = cosΞΈ. β΄ cos(x β Ο 2) = cos( Ο 2 βx) = sinx. OR. cos(A βB) = cosAcosB + sinAsinB. cos(x β Ο 2) = cosxcos( Ο 2) + sinxsin( Ο 2) cos(x β Ο 2) = cosx(0) +sinx(1) = 0 +sinx = sinx.
Cosinerule is also called law of cosines or Cosine Formula. Suppose, a, b and c are lengths of the side of a triangle ABC, then; a2 = b2 + c2 - 2bc cos β x. b2 = a2 + c2 - 2ac cos β y. c2 = a2 + b2 - 2ab cos β z. where β x, β y and β z are the angles between the sides of the triangle. The cosine rule relates to the lengths of the Toderive the derivative of cos x, we will use the following formulas: cos x = 1/sec x. sec x = 1/cos x. d (sec x)/dx = sec x tan x. tan x = sin x/ cos x. Using the above given trigonometric formulas, we can write the derivative of cos x and the derivative of 1/sec x, that is, d (cos x)/dx = d (1/sec x)/dx, and apply the quotient rule of Calculus Evaluate the Limit limit as x approaches pi/2 of sin (x) lim xβΟ 2 sin(x) lim x β Ο 2 sin ( x) Move the limit inside the trig function because sine is continuous. sin(lim xβΟ 2 x) sin ( lim x β Ο 2 x) Evaluate the limit of x x by plugging in Ο 2 Ο 2 for x x. sin( Ο 2) sin ( Ο 2) .