Cos A B Math
How to use the applet change angles a and b by pressing and buttons.
Cos a b math. Cos a b cos acosb sin asinb tan a b tan a tanb 1 tan atanb tan a b tan a tanb 1 tan atanb double angle formula sin 2a 2sin acos a cos 2a cos2 a sin2 a cos 2a 2cos2 a 1 1 2sin2 a tan 2a 2tan a 1 tan2 a half angle formula sin a 2 r 1 cos a 2 cos a 2 r 1 cos a 2 tan a 2 1 cos a sin a sin a 1 cos a product to sum cos acosb 1 2 cos a b cos a b sin asinb 1 2 cos a b cos a b sin acosb 1 2 sin a b sin a b. The line between the two angles divided by the hypotenuse 3 is cos b. To get the other two product to sum formulas add the two sine formulas from equation 48 and equation 49 or subtract them. That indicates the formula for sin a b.
In all mathematics book of 2 level in trigonometry chapter the proof is well available. The big angle a b consists of two smaller ones a and b the construction 1 shows that the opposite side is made of two parts. Cos a b cos a b sin a sin b. Cos a b cos a cos b sin a sin b.
Cos a b cos a cos b sin a sin b. We know cos 2a cos 2 a sin 2 a or we can write cos a a cosa cosa sina sina now replacing one a by b we can write cos a b cos a cosb sina sinb and hopefully it is proved. Cos a b cos a b 2 sin a sin b. This applet shows the formula for sin a b and cos a b.
I can try a proof working out in reverse order. The lower part divided by the line between the angles 2 is sin a.