Helen's Blog

Section 7-1

Converting:

convert degrees to rads: x pi/180

convert rads to degrees: x 180/pi

Section 10-1

Formulas:

sin(A+/-B)=sinA cosB+/ -cosA sinB

cos(A+/-B)=cosA cosB-/+sinA sinB

Examples:

1) Find the exact value of cos 75

cos(45+30)=cos 45 cos 30+ sin 45 sin 30
= (sq. root 2/2)(sq. root 3/2) + (sq. root 2/2)(1/2)
= Sq. root 6 + sq.root 2/4
2)simplify: cos 90 cos 45+sin 90 sin 45
= cos(90-45)
=cos 45
=sq. root 2/2