Question

prove

cos4A = 8sin^4(a) - 8sin^2(A) + 1

i've tried all sorts of methods but i just can't get the answer

Answer 1

@ganeshie8

Answer 2

is it cos (4a) ???

Answer 3

cos2x=2cos^2x-1

Answer 4

cos(2*(2a))
x=2a here

Answer 5

cos (2*(2a))=2cos^2(2a)-1

Answer 6

\[2(\cos2a)^2-1\]

Answer 7

cos2a=2cos ^2a-1

Answer 8

=2(2cos^2a-1)^2-1

Answer 9

yeah it is hang on i'll be looking through your working

Answer 10

but then it becomes 2(4cos^4A-1)^2-1

which i can't expand because it'll be expanding a power 4..

Answer 11

you dont how to open the square

Answer 12

cos^a=1-sin^a

Answer 13

2(2(1-sin^2a)-1)^2-1

Answer 14

=2(2-2sin^2a-1)^2-1
=2(1-2sin^2a)^2-1

Answer 15

2(1^2+(2sin^2a)^2-2*1*2sin^2a)-1
=2(1+4sin^4(a)-4sin^2a)-1
=2+8sin^4a-8sin^2a-1
=8sin^4a-8sin^2a+1

Answer 16

one thing i would like to say frn that if someone help u out thn its your responsibility to rply yes/no/ or anythimg else..not to sit like u r watching tv

Answer 17

well, thing is, you're posting every step one by one and its kind of infuriating because you can actually do them in fewer posts

i'm trying to process with information with each step, that's why i don't reply.

and since you're posting in that sequence for some reason —nobody else does that— i decided to just wait till you were done

but thank you for helping