Question

how to find the exact value of cos 7pi/4

Answer 1

*without a calculator

Answer 2

pi=180 degrees.

Answer 3

7*180=?

Answer 4

2 * pi radians is 1 whole trip around the unit circle. cos 7pi/4 = - cos pi/4. Can you draw the triangle in the unit circle for an angle of pi/4? you should be able to work out the rest with the Pythagorean theorem.

Answer 5

cos(7pi/4)
=cos[(8-1)pi/4]
=cos[8pi/4-1pi/4]
=cos[2pi-pi/4]
=cos(pi/4)
=cos(180/4)
=cos(45)
now you say the value.