Question

the value of cosπ/7 cos4π/7 cos5π/7​

Answer 1

Step-by-step explanation:

try the sum using below formulae before seeing the pic.

Cos5π/7 = -Cos2π/7

And now important thing in this type of question is to multiply and divide by 2Sinπ/7 so that in numerator we will get sin2π/7 and again by multiplying and dividing by 2 you get sin4π/7 and finally u will get sin8π/7

Answer 2

Step-by-step explanation:

cos 5π/7=-cos2π/7

cos 5π/7+cos2π/7=0

2cosπ*cos5π/7=0

-2cosπ/7=0