Given f be an odd function f(x)=3sinx+4cosx Now, f(6−11π)=3sin(6−11π)+4cos(6−11π)f(6−11π)=3sin(−2π+6π)+4cos(−2π+6π)f(6−11π)=3sin{−(2π−6π)}+4cos{−(2π−6π)}{ For odd functions sin(−θ)=−sinθ and cos(−θ)=−cosθ} ∴f(6−11π)=−3sin(2π−6π)−4cos(2π−6π)⇒f(6−11π)⇒f(6−11π) or f(6−11π)=+3sin(6π)−4cos6π=3×21−4×23=23−23