A=(cos36o-sin36o) (cos37o-sin38o)(cos42o-sin48o)
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NL
Nguyễn Lê Phước Thịnh
CTVHS
28 tháng 6
Vd5:
a: \(cos42^0=\sin\left(90^0-42^0\right)=\sin48^0\)
\(cos67^0=\sin\left(90^0-67^0\right)=\sin23^0\)
Ta có: \(23^0<30^0<38^0<48^0<75^0\)
=>Sin23<sin30<sin38<sin48<sin 75
=>cos67<sin30<sin38<cos42<sin75
b: \(\cot49^0=\tan\left(90^0-49^0\right)=\tan41^0\)
\(\cot50^0=\tan\left(90^0-50^0\right)=\tan40^0\)
Ta có: 25<27<40<41<80
=>tan25<tan27<tan40<tan41<tan80
=>tan25<tan27<cot49<cot50<tan80
Vd6:
a: \(\sin^2a+cos^2a=1\)
=>\(cos^2a=1-0,8^2=1-0,64=0,36=0,6^2\)
=>cosa=0,6
tan a=sin a/cosa
=0,8/0,6
=4/3
cot a=cosa/sin a
=0,6/0,8=3/4
b: \(\sin^2a+cos^2a=1\)
=>\(\sin^2a=1-0,6^2=1-0,36=0,64\)
=>sin a=0,8
tan a=sin a/cosa
=0,8/0,6
=4/3
cot a=cosa/sin a
=0,6/0,8=3/4
c: \(\tan a\cdot\cot a=1\)
=>\(\cot a=\frac13\)
\(1+\tan^2a=\frac{1}{cos^2a}\)
=>\(\frac{1}{cos^2a}=1+3^2=1+9=10\)
=>\(cos^2a=\frac{1}{10}\)
=>\(cosa=\frac{1}{\sqrt{10}}=\frac{\sqrt{10}}{10}\)
Ta có: \(\sin^2a+cos^2a=1\)
=>\(\sin^2a=1-\frac{1}{10}=\frac{9}{10}\)
=>\(\sin a=\frac{3}{\sqrt{10}}\)
d: \(\tan a\cdot\cot a=1\)
=>\(\tan a=\frac12\)
Ta có: \(1+\tan^2a=\frac{1}{cos^2a}\)
=>\(\frac{1}{cos^2a}=1+\left(\frac12\right)^2=1+\frac14=\frac54\)
=>\(cos^2a=\frac45\)
=>\(cosa=\frac{2}{\sqrt5}\)
\(\sin^2a+cos^2a=1\)
=>\(\sin^2a=1-\frac45=\frac15\)
=>\(\sin a=\frac{1}{\sqrt5}\)
NL
Nguyễn Lê Phước Thịnh
CTVHS
29 tháng 6
Vd5:
a: \(cos42^0=\sin\left(90^0-42^0\right)=\sin48^0\)
\(cos67^0=\sin\left(90^0-67^0\right)=\sin23^0\)
Ta có: 23<30<38<48<75
=>sin23<sin30<sin38<sin48<sin75
=>cos67<sin30<sin38<cos42<sin75
b: \(\cot49^0=\tan\left(90^0-49^0\right)=tan41^0\)
\(\cot50^0=\tan\left(90^0-50^0\right)=\tan40^0\)
Ta có: 25<27<40<41<80
=>tan 25<tan 27<tan 40<tan41<tan80
=>tan 25<tan27<cot49<cot50<tan80
Vd6:
a: \(\sin^2a+cos^2a=1\)
=>\(cos^2a=1-0,8^2=1-0,64=0,36=0,6^2\)
=>cosa=0,6
\(\tan a=\frac{\sin a}{cosa}=\frac{0.8}{0.6}=\frac43\)
\(\cot a=\frac{1}{\tan a}=1:\frac43=\frac34\)
b: \(\sin^2a+cos^2a=1\)
=>\(\sin^2a=1-0,6^2=1-0,36=0,64=0,8^2\)
=>sin a=0,8
\(\tan a=\frac{\sin a}{cosa}=\frac{0.8}{0.6}=\frac43\)
\(\cot a=\frac{1}{\tan a}=1:\frac43=\frac34\)
c: \(\tan a\cdot\cot a=1\)
=>\(\cot a=\frac13\)
Ta có: \(1+\tan^2a=\frac{1}{cos^2a}\)
=>\(\frac{1}{cos^2a}=1+3^2=10\)
=>\(cos^2a=\frac{1}{10}\)
=>\(cosa=\frac{1}{\sqrt{10}}\)
Ta có: \(\sin^2a+cos^2a=1\)
=>\(\sin^2a=1-\frac{1}{10}=\frac{9}{10}\)
=>\(\sin a=\frac{3}{\sqrt{10}}\)
d: \(\tan a\cdot\cot a=1\)
=>\(\tan a=\frac{1}{\cot a}=\frac12\)
Ta có: \(1+\tan^2a=\frac{1}{cos^2a}\)
=>\(\frac{1}{cos^2a}=1+\left(\frac12\right)^2=\frac54\)
=>\(cos^2a=\frac45\)
=>\(cosa=\frac{2}{\sqrt5}\)
Ta có: \(\sin^2a+cos^2a=1\)
=>\(sin^2a=1-\frac45=\frac15\)
=>sin a=\(\frac{1}{\sqrt5}\)
NL
Nguyễn Lê Phước Thịnh
CTVHS
29 tháng 6
Vd5:
a: \(cos42^0=\sin\left(90^0-42^0\right)=\sin48^0\)
\(cos67^0=\sin\left(90^0-67^0\right)=\sin23^0\)
Ta có: 23<30<38<48<75
=>sin23<sin30<sin38<sin48<sin75
=>cos67<sin30<sin38<cos42<sin75
b: \(\cot49^0=\tan\left(90^0-49^0\right)=tan41^0\)
\(\cot50^0=\tan\left(90^0-50^0\right)=\tan40^0\)
Ta có: 25<27<40<41<80
=>tan 25<tan 27<tan 40<tan41<tan80
=>tan 25<tan27<cot49<cot50<tan80
Vd6:
a: \(\sin^2a+cos^2a=1\)
=>\(cos^2a=1-0,8^2=1-0,64=0,36=0,6^2\)
=>cosa=0,6
\(\tan a=\frac{\sin a}{cosa}=\frac{0.8}{0.6}=\frac43\)
\(\cot a=\frac{1}{\tan a}=1:\frac43=\frac34\)
b: \(\sin^2a+cos^2a=1\)
=>\(\sin^2a=1-0,6^2=1-0,36=0,64=0,8^2\)
=>sin a=0,8
\(\tan a=\frac{\sin a}{cosa}=\frac{0.8}{0.6}=\frac43\)
\(\cot a=\frac{1}{\tan a}=1:\frac43=\frac34\)
c: \(\tan a\cdot\cot a=1\)
=>\(\cot a=\frac13\)
Ta có: \(1+\tan^2a=\frac{1}{cos^2a}\)
=>\(\frac{1}{cos^2a}=1+3^2=10\)
=>\(cos^2a=\frac{1}{10}\)
=>\(cosa=\frac{1}{\sqrt{10}}\)
Ta có: \(\sin^2a+cos^2a=1\)
=>\(\sin^2a=1-\frac{1}{10}=\frac{9}{10}\)
=>\(\sin a=\frac{3}{\sqrt{10}}\)
d: \(\tan a\cdot\cot a=1\)
=>\(\tan a=\frac{1}{\cot a}=\frac12\)
Ta có: \(1+\tan^2a=\frac{1}{cos^2a}\)
=>\(\frac{1}{cos^2a}=1+\left(\frac12\right)^2=\frac54\)
=>\(cos^2a=\frac45\)
=>\(cosa=\frac{2}{\sqrt5}\)
Ta có: \(\sin^2a+cos^2a=1\)
=>\(sin^2a=1-\frac45=\frac15\)
=>sin a=\(\frac{1}{\sqrt5}\)
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Đỗ Thanh Hải
CTVVIP
5 tháng 9 2021
11. A. cities/s/
12. A. begged d
13. A. approached t
14. A. laughs t
15. A. finished t
16. A. expanded id
17. A. expanded id
18. A. promised t
19. A. houses s
20. A. reduced s
21. A. cooked t
22. A. houses s
23. A. kites s
24. A. attacked t
25. A. possessed t
26. A. derived d
27. A. valued d
28. A. supported id
29. A. circled d
30. A. matched t
31. A. visited id
32. A. talked t
33. A. cursed t
34. A. approached t
\(A=\left(cos36-sin36\right)\left(cos37-sin38\right)\left(cos42-sin48\right)\)
\(\Leftrightarrow A=\left(cos36-sin36\right)\left(cos37-sin38\right)\left(cos42-sin\left(90-42\right)\right)\) \(\Leftrightarrow A=\left(cos36-sin36\right)\left(cos37-sin38\right)\left(cos42-cos42\right)=0\)