Seeking Mathematics Compulsory 4 Edition B People s Education Publishing House s Chapter 3 After cla

Generally not true.

cos（α+= cosαcosβ -sinαsinβ

Of course there is cos + cos = cos cos -sin sin

It was established. For example: =90°, =0° The above equation holds.

Induction formula used:

Induction formula. sin（－αsinα

cos（－αcosα

tan（－αtanα

cot（－αcotα

sin（π/2－α）cosα

cos（π/2－α）sinα

tan（π/2－α）cotα

cot（π/2－α）tanα

sin（π/2＋α）cosα

cos（π/2＋α）sinα

tan（π/2＋α）cotα

cot（π/2＋α）tanα

sin（π－sinα

cos（π－cosα

tan（π－tanα

cot（π－cotα

sin（π＋sinα

cos（π＋cosα

tan（π＋tanα

cot（π＋cotα

sin（3π/2－α）cosα

cos（3π/2－α）sinα

tan（3π/2－α）cotα

cot（3π/2－α）tanα

sin（3π/2＋α）cosα

cos（3π/2＋α）sinα

tan（3π/2＋α）cotα

cot（3π/2＋α）tanα

sin（2π－αsinα

cos（2π－αcosα

tan（2π－αtanα

cot（2π－αcotα

sin（2kπ＋αsinα

cos（2kπ＋αcosα

tan（2kπ＋αtanα

cot（2kπ＋αcotα

where k z).

Sum Angle Formula: Two Angles Sum Formula.

cos(α+=cosαcosβ-sinαsinβcos(α-=cosαcosβ+sinαsinβ

sin(α+=sinαcosβ+cosαsinβsin(α-=sinαcosβ -cosαsinβ

Directly using the above formula, it can be calculated:

1）cos75°=cos(30°+45°)

2）cos（-165°）=cos(165°)=cos(90+75)=-sin(75)=-sin(30+45)

3）cos7π/12=cos(π/2+)=-sin（π/12）=sin30°

4）cos（-61π/12）=cos（61π/12）=cos（5π+π/12）=cos（π+/12）=-cos(π/12)

Because the area of the open space is 9x5 = 45 square meters.

It takes 6x45=270 plants to have a monthly flower.

Chrysanthemum 8x45 = 360 plants.

Orchid 4x45 = 180 plants.

This is obviously wrong, AC is hypotenuse, how can it be equal to AB.