CMR Cho a lon hon b thì a/b+b/a lon hon 2
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Cho a lon hon 2, b lon hon 2.CMR ab lon hon a+b
cmr : a^2/b^2 +b^2/c^2+c^2/a^2 luon luon lon hon hoac bang c/b+ b/a+ a/c voi a,b,c lon hon 0
Cho 2 hinh chu nhat co cung dien tich .HInh 1 co kich thuoc a va b (a lon hon b) hinh 2 co kich thuoc c va d (c lon hon d) .chung minh rang nêu a lon hon c thi chu vi cua hinh1 lon hon chu vi hinh 2
Theo đề bài ta có \
\(\hept{\begin{cases}a>b;c>d\\ab=cd\\a>c\end{cases}}\)
\(\Rightarrow c>d>b\)(vì nếu \(d\le b\)thì \(ab>cd\))
Ta cần chứng minh
\(a+b>c+d\)
\(\Leftrightarrow\frac{cd}{b}+b>c+d\)
\(\Leftrightarrow cd+b^2>cb+db\)
\(\Leftrightarrow\left(cd-cb\right)+\left(b^2-db\right)>0\)
\(\Leftrightarrow\left(d-b\right)\left(c-b\right)>0\)(đúng)
\(\Rightarrow\)ĐPCM
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Tim cac so tu nhien A,B,C thoa man ca 2 dieu kien 20 nho hon A , nho hon B ,24 lon hon C lon hon B
\(20< A< B< C< 24\)
\(\Leftrightarrow A=21;B=22;C=23\)
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Theo đề bài ta có :
20 < A < B < C < 24
=> A = 21
B = 22
C = 23
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Cho a , b , c \(\in\)Z chung minh
a) với c khac 0 , ac = bc suy ra a = b
b) với c lon hon 0 , ac lon hon bc suy ra a lon hon b
a) Ta có :
\(ac=ab\Rightarrow ac-ab=0\Rightarrow c\left(a-b\right)=0\)
\(\Rightarrow a-b=0\)\(\left(c\ne0\right)\)
\(\Rightarrow a=b\)
b) Ta có:
\(ac>ab\Rightarrow ac-bc>0\)
\(\Rightarrow\left(a-b\right)c>0\)
\(\Rightarrow a-b>0\)
\(\Rightarrow a>b\)
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cho 3 số a b c biết tông 3 so do la so lon hon 1000 va nho hon 10000 so a lon hon so b 275 don vi so c hon so b 74 don vi xac dinh 3 so a b c
Cmr: /a+b/ lon hon hoac bang /a/+/b/
cho tap hop A la tap hop cac so tu nhien chan lon hon 20 va be hon 30 B la tap hop lon hon 2 va be hon 33 so phan tu thuoc tap hop C thuoc B ma khong thuoc A
cho a,b,c la do dai 3 canh tam giac. cmr: can 3(a-c)(b-a)(c-b)/a.b.c lon hon bang 1/2