285:245=???????????????
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LH
2
28 tháng 6 2021
Ta có: \(A=\sin^25^0+\sin^225^0+\sin^245^0+\sin^265^0+\sin^285^0\)
\(=\left(\sin^25^0+\sin^285^0\right)+\left(\sin^225^0+\sin^265^0\right)+\dfrac{1}{2}\)
\(=2+\dfrac{1}{2}=\dfrac{5}{2}\)
28 tháng 6 2021
\(\Rightarrow A=\left(sin^25^0+sin^285^0\right)+\left(sin^225^0+sin^265^0\right)+sin^245^0=\left(sin^25^0+cos^25^0\right)+\left(sin^225^0+cos^225^0\right)+\dfrac{1}{2}=1+1+\dfrac{1}{2}=\dfrac{5}{2}\)
VT
30 tháng 9 2019
sina=cos(90-a) thay vào ta được
sin215+sin225+sin235+cos235+cos225+cos215=3
tương tự câu dưới ta được =3/2
HN
11 tháng 9 2019
\(A=\left(\sin^25^0+\sin^285^0\right)+\left(\sin^225^0+\sin65^0\right)+\sin^245^0\)
\(=\left(\sin^25^0+\cos^25^0\right)+\left(\sin^225^0+\cos^225^0\right)+\frac{1}{2}\)
\(=1+1+\frac{1}{2}\)
\(=\frac{5}{2}\)
HN
11 tháng 9 2019
\(B=\left(\tan1^0.\tan89^0\right).\left(\tan2^0.\tan88^0\right).\left(\tan3^0.\tan87^0\right)...\tan45^0=\left(\tan1^0.\cot1^0\right).\left(\tan2^0.\cot2^0\right).\left(\tan3^0.\cot3^0\right)...1=1\)
22 tháng 7 2018
Bài 1 :
\(D=cos^220^0+cos^230^0+cos^240^0+cos^250^0+cos^260^0+cos^270^0\)
\(=\left(cos^220^0+cos^270^0\right)+\left(cos^230^0+cos^260^0\right)+\left(cos^240^0+cos^250^0\right)\)
\(=1+1+1=3\)
Bài 2 :
\(E=sin^25^0+sin^225^0+sin^245^0+sin^265^0+sin^285^0\)
\(=\left(sin^25^0+sin^285^0\right)+\left(sin^225^0+sin^265^0\right)+sin^245^0\)
\(=1+1+\dfrac{1}{2}=\dfrac{5}{2}\)
Bài 3 :
\(F=sin^6\alpha+cos^6\alpha+3sin^2\alpha.cos^2\alpha\)
\(=1-3sin^2\alpha.cos^2\alpha+3sin^2a.cos^2\alpha\)
\(=1\)
PT
1
CM
17 tháng 9 2019
a, 6100 + 2900
= (6000 + 2000) + (100 + 900)
= 8000 + 1000 = 9000
b, 7825 + 1075
= (7000 + 1000) + 800 + (25 + 75)
= 8000 + 800 + 100
= 8900
c, 285 + 285 + 285 + 285 = 285 × 4 = 1140
d, 2345 + 1745
= (2000 + 1000) + (300 + 700) + (45 + 45)
= 3000 + 1000 + 90
= 4090
NT
0
25 tháng 2 2017
We can choose our friends, but we cannot choose our relatives. That does not mean that members of our family cannot also be our friends. Many children have a very good relationship with their parents and they see them as friends. Of course when you are teenager, there are time that you do not get on very well with their parents, or they can get angry with you. That only natural. There are times you want to be independent and decide things by yourself. After that, nobody perfect and we all make mistakes. But your parents understand that. When you grown up, ou will see that you have many things in common with your mum and dad and you will be closer to them.
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