Verify this trigonometrical identity?
Question Show that cos^4(x)-sin^4(x)=cos(2x) Answer We use the identities below. (you should know them by heart) sin^2(x) + cos^2(x) = 1 …(1) cos(2x)= 2cos^2(x) – 1 …(2) Put (2) into (1) from which we get, cos(2x) = 2cos^2(x) – [sin^2(x) + cos^2(x) ] = cos^2(x) – sin^2(x) simplyfying = [cos^2(x) – sin^2(x)]*[sin^2(x) + cos^2(x)]...
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