Find the exact value for cos 7𝜋/ 12 applying sum and difference formulas involving 𝜋 /3 and 𝜋/ 4 .

Question

shouldn't the answer be -0.2588/-0.259. If that's not the correct answer what is?

Answer 1

cos(θ+φ) = cos(θ)cos(φ) - sin(θ)sin(φ)

where the sum is 7pi/12 and θ and φ are pi/4 and pi/3 respectively.

(you can check it all with a calculator set to radians)

Please consider a tutor. Take care.