câu b nha mn
K
Khách
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9 tháng 10 2021
b: Xét ΔABH vuông tại H có
\(AB^2=AH^2+HB^2\)
hay AH=12(cm)
Xét ΔAHB vuông tại H có
\(\sin\widehat{B}=\cos\widehat{C}=\dfrac{AH}{AB}=\dfrac{12}{13}\)
\(\cos\widehat{B}=\sin\widehat{C}=\dfrac{5}{13}\)
\(\tan\widehat{B}=\cot\widehat{C}=\dfrac{12}{5}\)
\(\cot\widehat{B}=\tan\widehat{C}=\dfrac{5}{12}\)
N
18 tháng 11 2021
a. \(I=I1=I23=U:R=6:\left(1,8+\dfrac{3\cdot2}{3+2}\right)=2A\left(R1ntR23\right)\)
\(\rightarrow U1=I1\cdot R1=2\cdot1,8=3,6V\)
\(\rightarrow U23=U2=U3=I23\cdot R23=2\cdot\left(\dfrac{3\cdot2}{3+2}\right)=2,4V\left(R1//R2\right)\)
\(\Rightarrow\left\{{}\begin{matrix}I2=U2:R2=2,4:3=0,8A\\I3=U3:R3=2,4:2=1,2A\end{matrix}\right.\)
b. \(\left\{{}\begin{matrix}Q_{toa1}=A_1=U_1\cdot I_1\cdot t=3,6\cdot2\cdot1\cdot60=432\left(J\right)\\Q_{toa2}=A_2=U_2\cdot I_2\cdot t=2,4\cdot0,8\cdot1\cdot60=115,2\left(J\right)\end{matrix}\right.\)
câu 9 sẽ kco nhé mn, mn giúp mình hoàn thiện xong nhanh nha, mn có thể làm bnhieu câu trở lên cũng đc nha 
mn ui bày mk nha củm mơn mn nhìu
NV
Nguyễn Việt Lâm
Giáo viên
2 tháng 11 2021
Tất cả k dưới đây là \(k\in Z\)
1.
ĐKXĐ: \(1-2cosx\ne0\Rightarrow cosx\ne\dfrac{1}{2}\)
\(\Rightarrow x\ne\pm\dfrac{\pi}{3}+k2\pi\)
2.
\(cos2x-1=0\Rightarrow cos2x=1\)
\(\Rightarrow2x=k2\pi\)
\(\Rightarrow x=k\pi\)
b.
\(\sqrt{3}cotx-3=0\Rightarrow cotx=\sqrt{3}\)
\(\Rightarrow x=\dfrac{\pi}{6}+k\pi\)
c.
\(2sin^22x+sin2x-1=0\)
\(\Rightarrow\left[{}\begin{matrix}sin2x=-1\\sin2x=\dfrac{1}{2}\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}2x=-\dfrac{\pi}{2}+k2\pi\\2x=\dfrac{\pi}{6}+k2\pi\\2x=\dfrac{5\pi}{6}+k2\pi\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=-\dfrac{\pi}{4}+k\pi\\x=\dfrac{\pi}{12}+k\pi\\x=\dfrac{5\pi}{12}+k\pi\end{matrix}\right.\)
3.
Theo điều kiện có nghiệm của pt lượng giác bậc nhất, pt đã cho có nghiệm khi:
\(\sqrt{3}^2+2^2\ge m^2\)
\(\Rightarrow m^2\le7\)
\(\Rightarrow-\sqrt{7}\le m\le\sqrt{7}\)
TV
4
TV
1
DT
Đỗ Thanh Hải
CTVVIP
5 tháng 11 2021
2 she had got the price of the contest, she would be happy now
3 I had gone to the concert last night ,I would be tired
4 John had finished all his homework, he could see a movie now
5 we had listened to my mother, we wouldn't be in trouble right now
Ex5
1 you arrive at the offcie earlier than I do, please turn on the air-conditioner
2 Were it not snowy, the children would go to school
3 he not died so young, he would be a famous musician
4 Were I you, I would take care of my car
5 not very bad-tempered, his wife would give him soon are marrage
6 Had she not got married at such an early age, he would be at university
XV
0