Here are some formulae tht u dont see often

tan(A+B+C)= tanA+tanB+tanC-tanAtanBtanC
                    1-tanAtanB-tanBtanC-tanAtanC 

cosAcos2Acos4A.....n terms=sin(2ⁿA) / 2ⁿ.sinA   (divide and multiply by sinA)

sinA+sin(A+B)+sin(A+2B).....to n terms = sin nB/2 x sin[A+(n-1)B/2]
                                                                          sinB/2

cosA+cos(A+B)+cos(A+2B)....n terms = sin nB/2 x cos[A+(n-1)B/2]
                                                                          sinB/2

sinA+sin2A+sin3A......n terms= sin nA/2 x sin[(n+1)A/2]
                                                            sin A/2

cosA+cos2A+cos3A......n terms= sin nA/2 x cos[(n+1)A/2]
                                                            sin A/2

If A+B+C= thn :

sin2A +sin2B+sin2C=4sinAsinBsinC
1+cos2A= - 4cosAcosBcosC
sinA=4cosA/2cosB/2cosC/2
cosA=1+4sinA/2sinB/2sinC/2
tanA= tanA
cotBcotC=1
cotA/2=cotA/2
tanA/2tanB/2=1

a/sinA=b/sinB=c/sinC (sine law)
a²=b² + c² -2 b.c cosA (cosine law)
a=b.cosC+c.cosB (projection formula)
tan B-C = b-c x cotA/2
       2      b+c
sinA/2=  {(s-b)(s-c)/bc}
cosA/2=s(s-a)/bc
=s(s-a)(s-b)(s-c)=abc/4R
r=4R sinA/2
r1=/(s-a)
r2=/(s-b)
r3=/(s-c)