Question

if sin a = 1/2 then prove that (3cos a - 4cos cubic a) = 1​

Answer 1

Step-by-step explanation:

sin a=1/2

so

3cos a - 4cos^3 a

cos a(3-4cos^2a)

cosa(3-3cos^2a-cos^2a)

cosa(3(1-cos^2a)-cos^2a)

cosa(3sin^2a-cos^2a)

cosa(3/4-cos^2a)

put cosa value and get answer

Answer 2

answer:

3cos a - 4cos³a=1--------------------------(i)

Step-by-step explanation:

• if sin a =1/2
• a=30°
• by putting value of a in equation (i) we get,
• 3cos30°–4cos³30°
• 3(√3/2)–4(√3/2)³
• 3√3/2 – 12√3/8
• 12√3/8 – 12√3/8
• =0
• so this is wrong
• thank u