Question

sin (70°+o)cos (20°-o)=0​

Answer 1

Answer:

sin (70)- cos(20)

sin (70)- cos(90-70)

sin (70)- sin (70)

=0

Answer 2

[sin(70) cos0 + cos(70) sin0][cos(20) cos0 - sin(20) sin0] = 0

[sin (70) × 1 + cos (70) × 0][cos (20) × 1 - sin (20) × 0] = 0

(sin 70 )(cos 20) = 0

sin(90-20) cos (20) = 0

(cos 20)(cos 20) = 0

cos²20 = 0

=> cos 20 = 0