Question

Evaluate the following: `((sin3θ - 2sin4θ))/((cos3θ - 2cos4θ))` when 2θ = 30°

Answer 1

2θ = 30°
⇒ θ = 15°

∴ `(sin3θ - 2sin4θ)/(cos3θ - 2cos4θ)`

= `(sin3 xx 15° - 2sin4 xx 15°)/(cos3 xx 15° - 2cos"4 xx 15°)`

= `"(sin45° - 2sin60°)/(cos45° - 2cos60°)`

= `(1/sqrt(2) - 2 xx sqrt(3)/(2))/((1)/sqrt(2) - 2 xx (1)/(2))`

= `(1/sqrt(2) - sqrt(3))/(1/sqrt(2) - 1)`

= `((1 - sqrt(6))/(sqrt(2)))/((1 - sqrt(2))/(sqrt(2)`

= `(1 - sqrt(6))/(1 - sqrt(2))`

= `(1 - sqrt(6))/(1 - sqrt(2)) xx (1 + sqrt(2))/(1 + sqrt(2)`

= `(1 + sqrt(2) - sqrt(6) - sqrt12)/(1 - 2)`

= `(1 + sqrt(2) - sqrt(6) - 2sqrt(3))/(-1)`

= `2sqrt(3) + sqrt(6) - sqrt(2) - 1`.