Sunday

February 1, 2015

February 1, 2015

Posted by **Anonymous** on Saturday, October 31, 2009 at 12:06pm.

use an equivalent trigonometric expression to show that

cos pie/3 = 1/2.

- math -
**Reiny**, Saturday, October 31, 2009 at 12:36pmFirst of all

sin pi/6 = 1/2 not 1/3,

recall that cos 2A = 1 - 2sin^2 A

then

sin pi/3 = 1 - 2(1/2)^2

= 1 - 2(1/4)

= 1 - 1/2

= 1/2

Or we could use the fact that

cos (theta) = sin (pi/2 - theta)

cos pi/3 = sin (pi/2 - pi/3)

= sin pi/6

= 1/2

or

since we can get both sines and cosine values by knowing that ratios of sides of the 30-60-90 triangle, we could have just stated that cos pi/3 or cos 60º = 1/2, just like they found

sin pi/6 = 1/2

**Answer this Question**

**Related Questions**

Calculus grade 12 - solve for (<_ = less than or equal to / pie = pie sign...

maths - Choose the two options which are true for all values of x 1) cos (x) = ...

math - evaluate the expressions below and leave them in radical form. 1. sin(pie...

physics - The motion of a particle is described by x = 10 sin (piet +pie/2 ). At...

calculus - Hi i have two questions: what is the exact value of cos 5(pie)/12? ...

Algebra II - Multiple Choice (theta) means the symbol 0 with the dash in it. 1.)...

maths - prove that sin sqared pie/6+ cos sqared pie/3-tansqare pie/4=1/2 in ...

maths - Choose three options which are true: a) an angle of 150 degrees is ...

Math (College Level Mathematics) - Fourier cosine series correspondence for f(x...

precal - use the half angle formula to determine the exact values of sin, cos, ...