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sin^4(3π/8)-cos^4(3π/8)
=[sin^2(3π/8)-cos^2(3π/8)]*[sin^2(3π/8)+cos^2(3π/8)]
=[sin^2(3π/8)-cos^2(3π/8)]*1
=[sin^2(3π/8)-cos^2(3π/8)]
=-cos[2*(3π/8)]
=-cos3π/4
=√2/2
=[sin^2(3π/8)-cos^2(3π/8)]*[sin^2(3π/8)+cos^2(3π/8)]
=[sin^2(3π/8)-cos^2(3π/8)]*1
=[sin^2(3π/8)-cos^2(3π/8)]
=-cos[2*(3π/8)]
=-cos3π/4
=√2/2
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