How to deduce sin (π / 2 + α) = cos α sin（π/2＋α）＝cosα cos（π/2＋α）＝－sinα sin（π/2－α）＝cosα cos（π/2－α）＝sinα All of them

How to deduce sin (π / 2 + α) = cos α sin（π/2＋α）＝cosα cos（π/2＋α）＝－sinα sin（π/2－α）＝cosα cos（π/2－α）＝sinα All of them

1. Left = sin π / 2cos α + cos π / 2Sin α = 1 * cos α + 0 * sin α = cos α = right
2. Left = cos π / 2cosa sin π / 2sina = 0 * cosa-1 * Sina = - Sina = right
3. Left = sin π / 2cosa cos π / 2sina = 1 * cosa-0 * Sina = cosa = right
4. Left = cos π / 2cosa + sin π / 2sina = 0 * cosa + 1 * Sina = Sina = right
It is the application of sum angle formula

cos^2 15°-sin^2 15°=

=Method 1: (COS ^ 2) 15 ° - (sin ^ 2) 15 = (cos15 + sin15) (cos15-sin15) = [sin (90-15) + sin15] [sin (90-15) - sin15] = (sin75 + sin15) (sin75-sin15) = 2 * sin (75 + 15) / 2 * cos (75-15) / 2 * 2 * cos (75 + 15) * sin (75-15) / 2 = 4 * sin45 * cos30 * cos45

sin(a+45°)sin(a+15°)+cos(a+45°)cos(a+15°)

sin(a+45°)sin(a+15°)+cos(a+45°)cos(a+15°)
=cos(a+45°)cos(a+15°)+sin(a+45°)sin(a+15°)
=cos[(a+45°)-(a+15°)]
=cos(a+45°-a-15°)
=cos30°
=√3/2

Find (sin ^ 2) 15 degree (COS ^ 2) 15 degree

(sin^2)15°(cos^2)15°=(sin15°cos15°)^2=(sin30°/2)^2=(1/4)^2=1/16

The value of sin ^ 2 15 ° - cos ^ 2 15 ° is
A.-√3/2 B.1/2 C.-1/4 D.3/4

The original formula = - (COS ^ 2 15 ° - Sin ^ 2 15 °)
=-Cos30 degree
=-√3/2
Choose a

The value of sin ^ 2 (15 °) - cos ^ 2 (15 °) is

Original = - (COS & # 178; 15 Sin & # 178; 15)
=-cos30
=-√3/2

The value of COS ^ 2 15 ° - Sin ^ 2 15 °

Original formula = cos30 degree
=√3/2

If cos (75 ° + α) = 1 / 3, then the value of sin (15 ° - α) is obtained

∵90°-（75°+α）=15°-α
∴cos（75°+α）=sin（15°-α）
∴sin（15°-α）=1/3

What is the DWT unit on the scale

Calculated dynamic weight value (total weight of tipping bucket and material)

In CAD acadiso.dwt And acad.dwt What's the difference?

AutoCAD provides two linetype files, which are in the "support" subfolder of the main folder of AutoCAD“ acad.lin ”And“ acadiso.lin ”, respectively“ acad.dwt ”And“ acadiso.dwt ”Called when creating a file. The types of linetypes defined in the two files are the same, except that the sizes of the linetypes are slightly different