\cos ^{3} 10^{0}+\cos ^{3} 110^{0}+\cos ^{3} 130^{\circ}=\begin{array}

1.	\cos ^{3} 10^{0}+\cos ^{3} 110^{0}+\cos ^{3} 130^{\circ}=\begin{array}{ll}{\text { A) } \frac{3}{4}} & {\text { B) } \frac{3}{8}}\end{array} B \frac{3 \sqrt{3}}{8} \quad \text { D) } \frac{3 \sqrt{3}}{4}
Answer» Cos³ x + Cos ³ ( 120-x )+Cos³ ( 120+ x ) = (3/4)Cos 3x____________________________ According to the problem given , x = 10 , Cos³ 10 + Cos³ 110+Cos³130 = Cos10+ Cos³ (120-10)+ Cos³ (120+10) = ( 3/4) Cos (3×10) = (3/4)Cos30° = (3/4)×(√3/2) = (3√3)/8

\cos ^{3} 10^{0}+\cos ^{3} 110^{0}+\cos ^{3} 130^{\circ}=\begin{array}{ll}{\text { A) } \frac{3}{4}} & {\text { B) } \frac{3}{8}}\end{array} B \frac{3 \sqrt{3}}{8} \quad \text { D) } \frac{3 \sqrt{3}}{4}

Answer»

Cos³ x + Cos ³ ( 120-x )+Cos³ ( 120+ x )

= (3/4)Cos 3x____________________________

According to the problem given ,

x = 10 ,

Cos³ 10 + Cos³ 110+Cos³130

= Cos10+ Cos³ (120-10)+ Cos³ (120+10)

= ( 3/4) Cos (3×10)

= (3/4)Cos30°

= (3/4)×(√3/2)

= (3√3)/8