Pt lượng giác

Y

youaremysoul

a.
pt \Leftrightarrow $cos2x - 3sinx = 1 + 2sinx$

\Leftrightarrow $1 - 2sin^2x - 3sinx = 1 + 2sinx$

\Leftrightarrow $2sin^2x + 5sinx = 0$

b,
bạn cm: $cos^6x + sin^6x = \dfrac{5}{8} + \dfrac{3}{8}cos4x$

khi đó pt
\Leftrightarrow $\dfrac{5}{8} + \dfrac{3}{8}cos4x = \dfrac{4(1 + cos4x)}{2}$

\Leftrightarrow $5 + 3cos4x = 16 + 16cos4x$

\Leftrightarrow $13cos4x = -11$

c,
pt \Leftrightarrow $-1 + 4(1 - cos^2x) = 4cos^4x$

\Leftrightarrow $4cos^4x + 4cos^2x - 3 = 0$

d,
pt \Leftrightarrow $3cosx + cos2x - cos3x + 1 - (cosx - cos3x) = 0$

\Leftrightarrow $2cosx + 2cos^2x - 1 + 1 = 0$

\Leftrightarrow $2cos^2x + 2cosx = 0$
 
You must log in or register to reply here.
Top Bottom