Question

Fill in the blanks. 

i. sin 20° = cos ....°

ii. tan 30° x tan = ...° = 1

iii. cos 40° = sin ...°

Answer 1

i. sin 20° 

= cos (90° – 20°) ...[∵ sin θ = cos(90 – θ)] 

= cos 70° 

ii. tan θ x tan(90 – θ) = 1 

Substituting θ = 30°, tan 30° x tan(90 – 30)° = 1 

∴ tan 30° x tan 60° = 1 

iii. cos 40° 

= sin(90° – 40°) …[∵ cos θ = sin(90 – θ)] 

= sin 50°