Question

упростите выражение.
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Answer 1

Ответ:     $\dfrac{3}{4}$   .

$\star \ \ sin^2a+cos^2a=1\ \ \to \ \ \ (sin^2a+cos^2a)^2=1^2\ \ ,\\\\sin^4a+2\, sin^2a\cdot cos^2a+cos^4a=1\\\\sin^4a+cos^4a=1-2\, sin^2a\cdot cos^2a\\\\sin^4a+cos^4a=1-2\cdot (\underbrace{sina\cdot cosa}_{\frac{1}{2}\cdot sin2a})^2\\\\sin^4a+cos^4a=1-2\cdot \dfrac{1}{4}\, sin^22a\\\\sin^4a+cos^4a=1-\dfrac{1}{2}\, sin^22a\ \ \ \star \\\\\\sin^4a+cos^4a-\dfrac{1}{4}\, cos4a=1-\dfrac{1}{2}\, sin^22a-\dfrac{1}{4}\cdot (cos^22a-sin^22a)=$

$=1-\dfrac{1}{2}\, sin^22a-\dfrac{1}{4}\cdot cos^22a+\dfrac{1}{4}\, sin^22a=1-\dfrac{1}{4}\, sin^22a-\dfrac{1}{4}\cdot cos^22a=\\\\=1-\dfrac{1}{4}\cdot (\underbrace{sin^22a+cos^22a}_{1})=1-\dfrac{1}{4}=\dfrac{3}{4}$