Question

rút gọn bt A = sin⁴ +sin².cos² + cos⁴

Answer 1

\(=\left(sin^2a+cos^2a\right)^2-2\cdot sin^2a\cdot cos^2a\left(sin^2a+cos^2a\right)+sin^2a\cdot cos^2a\)

\(=1-sin^2a\cdot cos^2a=1-\dfrac{1}{4}sin^22a\)