arctan7 + 2.arccot1/3=?

Dik üçgenlerden:

Arctan7=A ise sinA=7/√50 ve cosA=1/√50

Arccot=1/3 ise sinB=3/√10 ve cosB=1/√10

sin(A+2B)=sinA.cos2B+sin2B.cosA

=sinA[2(cosB)²-1]+2sinB.cosB.cosA

=[7/√50][2(1/10)-1]+2(3/10)(1/√50)

=-56/[10√50]+6/[10√50]

=-50/[10√50]

=-√50/10

=-√2/2 ise A+2B=225 veya 315