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The Brainliest Answer!
2015-02-24T09:26:31+05:30
Let two vector
a = 4 unit
b = 5 unit
angle α = 60
R = √(a²+b²+2abcosα)
   = √(4²+5²+2*4*5*cos60)
   = √(16+25+40/2)
   = √(61)  unit
tanβ = bsinα / (a+bcosα)
        = 5*√3/2 / (4+5*1/2)
       = 5*√3/2 / (13/2)
tanβ = 5√3/13
β = tan^-1(5√3/13)
1 5 1