Question

giúp vs

 

Answer 1

12B

13D

14B

15C

16C

17:

\(3cosx+2=0\)

=>\(cosx=-\dfrac{2}{3}\)

=>\(\left[{}\begin{matrix}x\simeq132^0+k\cdot360^0\\x\simeq-132^0+k\cdot360^0\end{matrix}\right.\)

TH1: \(x=132^0+k\cdot360^0\)

\(-450< =x< =450\)

=>\(-582^0< =k\cdot360^0< =318^0\)

=>\(-\dfrac{97}{60}< =k< =\dfrac{53}{60}\)

=>\(k\in\left\{-1;0\right\}\)

=>Có 2 nghiệm

TH2: \(x=-132^0+k\cdot360^0\)

\(-450< =x< =450\)

=>\(-318< =k\cdot360< =582\)

=>\(-\dfrac{318}{360}< =k< =\dfrac{582}{360}\)

=>\(k\in\left\{0;1\right\}\)

=>Có 2 nghiệm

=>Chọn D