Trigonometry 快少少

1.cos60cos30 +sin60cos30
= (1/2)(√3/2) + (√3/2)(√3/2)
= √3/4 + 3/4
= (3 + √3) / 4


2009-10-11 16:38:41 補充：
Method 1 :
cos60cos30 +sin60sin30

= (1/2)(√3/2) + (√3/2)(1/2)

= √3 / 2

Method 2 :

cos60cos30 + sin60sin30

= sin(90-60) sin(90-30) + sin60sin30

= sin30sin60 + sin60sin30

= 2sin30sin60

= 2(1/2)(√3/2)

= √3 /2

2009-10-11 16:39:11 補充：
Method 3 : cos(a - b) = cosa cosb + sina sinb

cos(60 - 30) = cos60 cos30 + sin60 sin30

cos 30 = cos60 cos30 + sin60 sin30

√3 / 2 = cos60 cos30 + sin60 sin30

cos(A+B)=cosAcosB-sinAsinB

cos(A-B)=cosAcosB+sinAsinB

cos60cos30+ sin60sin30

=cos(60-30)

=cos30

=√3/2

cos60cos30+sin60sin30

=cos(60-30)

=cos30

=√3/2//