Question

1-2 sin e cos 20-2 sin 40 = cos (20)

Answer 1

Answer:

No this is not the same as cos(2Ф)

Step-by-step explanation:

First I changed the $cos^{2}$Ф into 1-$sin^{2}$Ф

I then foiled the (1-2$sin^{2}$Ф)(1-$sin^{2}$Ф) and that resulted in 1-$sin^{2}$Ф-2$sin^{2}$Ф+2$sin^{4}$Ф

From there, I then cancelled the two 2$sin^{4}$Ф and combined like terms and was left with 1-3$sin^{2}$Ф

Now 1-3$sin^{2}$Ф ≠ cos(2Ф)