👤

AJUTOOOOOOOR!!!!!!!!Sa se calculeze tgx ,stiind ca x∈(3π/4 , π) si sin2x= -3/5.

Răspuns :

sin 2x=2tgx/(1+tg²x)
notand tgx=t , avem
-3/5=2t/(1+t²)
10t=-3-3t²
3t²+10t+3=0

t1,2=(-10+-√(100-36))/6= (-10+-√54)/6= (-10+-8)/6
t1=-3
t2=-1/3
x∈(3π/4; π)⇒tgx∈(0;-1) deci convine t2
tgx=-1/3