(i) In any ΔABC, prove that sin(B−C)sin(B+C)=b2−c2a2 (ii) Prove t

1.	(i) In any ΔABC, prove that sin(B−C)sin(B+C)=b2−c2a2 (ii) Prove that cos A cos(60∘−A)cos(60∘+A)=14cos3A Or Find the value of (i) tan13π12 (ii) sin360∘ (iii) cos18∘
Answer» (i) In any $Δ A B C$ , prove that $\frac{s i n (B - C)}{s i n (B + C)} = \frac{b^{2} - c^{2}}{a^{2}}$ (ii) Prove that $c o s A c o s (60^{\circ} - A) c o s (60^{\circ} + A) = \frac{1}{4} c o s 3 A$ Or Find the value of $(i) t a n \frac{13 π}{12}$ $(i i) s i n 360^{\circ}$ $(i i i) c o s 18^{\circ}$

(i) In any ΔABC, prove that sin(B−C)sin(B+C)=b2−c2a2 (ii) Prove that cos A cos(60∘−A)cos(60∘+A)=14cos3A Or Find the value of (i) tan13π12 (ii) sin360∘ (iii) cos18∘

Answer»

(i) In any $Δ A B C$ , prove that $\frac{s i n (B - C)}{s i n (B + C)} = \frac{b^{2} - c^{2}}{a^{2}}$

(ii) Prove that $c o s A c o s (60^{\circ} - A) c o s (60^{\circ} + A) = \frac{1}{4} c o s 3 A$

Find the value of

$(i) t a n \frac{13 π}{12}$

$(i i) s i n 360^{\circ}$

$(i i i) c o s 18^{\circ}$