In this question
Deduce
cos4a = 8(cosa)^4 - 8(cosa)^2 + 1
hence solve
8x^4 - 8x^2 +1 = 0
Ive done all except this part:
Deduce exact values of cos(pi/8) and cos (5pi/8)
Im using sum and product of roots and im getting
cos^2(5pi/8)cos^2(pi/8) = 1 and cos^2(5pi/8) + cos^2(pi/8) = 1
But i cannot solve simultaneously as quadratic resulting will give me imaginary.. Why cant i do that?
Deduce
cos4a = 8(cosa)^4 - 8(cosa)^2 + 1
hence solve
8x^4 - 8x^2 +1 = 0
Ive done all except this part:
Deduce exact values of cos(pi/8) and cos (5pi/8)
Im using sum and product of roots and im getting
cos^2(5pi/8)cos^2(pi/8) = 1 and cos^2(5pi/8) + cos^2(pi/8) = 1
But i cannot solve simultaneously as quadratic resulting will give me imaginary.. Why cant i do that?