goi a,b,c la 3 canh cua ΔABC
biet \(\left(1+\frac{b}{a}\right)\left(1+\frac{c}{b}\right)\left(1+\frac{a}{c}\right)=\)8
cm ΔABC deu
Gọi a, b, c là độ dài 3 cạnh của ΔABC. Biết \(\left(1+\frac{b}{a}\right)\left(1+\frac{a}{c}\right)\left(1+\frac{c}{b}\right)=8\). C/m ΔABC đều.
Ta có:
(1 + b/a)(1 + c/b)(1 + a/c) = 8
<=> (a + b)/a.(b + c)/b.(c + a)/c = 8
<=> (a + b)(b + c)(c + a) = 8abc
Áp dụng bất đẳng thức Cauchy cho các số dương a, b, c ta được:
a + b ≥ 2√(ab)
b + c ≥ 2√(bc)
c + a ≥ 2√(ca)
=> (a + b)(b + c)(c + a) ≥ 8√(a^2.b^2.c^2) = 8|abc| = 8abc (vì a, b,c > 0)
Dấu "=" xảy ra <=> a = b; b = c; c = a <=> a = b = c <=> ΔABC đều
https://olm.vn/hoi-dap/detail/2293581520.html cậu tham khảo nhé !
1.tìm các nghiem nguyen cua phuong trinh: 54x^3+1=y^3
2.cho x+y=1 và xy khac 0.chung mih \(\frac{x}{y^3-1}+\frac{y}{x^3-1}+\frac{2\left(x-y\right)}{x^2y^2+3}=0\)
3.cho a,b,c la cac so thuc duong.chung minh :\(\left(\frac{a}{b+c}+\frac{b}{a+c}+\frac{c}{a+b}\right)^2+\frac{14abc}{\left(a+b\right)\left(b+c\right)\left(c+a\right)}\ge4\)
Câu 2 thế y = 1 - x rồi quy đồng như bình thường là ra bn nhé
\(\frac{1}{a\left(a-b\right)\left(a-c\right)}+\frac{1}{b\left(b-a\right)\left(b-c\right)}+\frac{1}{c\left(c-a\right)\left(c-b\right)}\) giup mik vs de bai la thuc hien phep tinh nhe
Goi a,b,c là 3 cạnh của 1 tam giác và ha , hb , hc là các đường cao tương ứng
Chứng minh hệ thức
\(\left(a+b+c\right)\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)=\left(ha+hb+hc\right)\left(\frac{1}{ha}+\frac{1}{hb}+\frac{1}{hc}\right)\)
Gọi S là diện tích của tam giác
Ta có :
\(a=\frac{2S}{h_a};b=\frac{2S}{h_b};c=\frac{2S}{h_c}\)
\(\Rightarrow\left(a+b+c\right)\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)=\left(a+b+c\right)\left(\frac{h_a+h_b+h_c}{2S}\right)\)
\(=\left(h_a+h_b+h_c\right).\frac{a+b+c}{2S}=\left(h_a+h_b+h_c\right)\left(\frac{1}{h_a}+\frac{1}{h_b}+\frac{1}{h_c}\right)\)
=> đpcm
1)\(\frac{1}{\left(a-b\right)\left(a-c\right)}+\frac{1}{\left(b-c\right)\left(b-a\right)}+\frac{1}{\left(c-a\right)\left(c-b\right)}\)
2)\(\frac{a^2}{\left(a-b\right)\left(a-c\right)}+\frac{b^2}{\left(b-c\right)\left(b-a\right)}\frac{c^2}{\left(c-a\right)\left(c-b\right)}\)
3)\(\frac{1}{x^2+3x+2}+\frac{2x}{x^3+4x^2+4x}+\frac{1}{x^2+5x+6}\)
các bạn làm được ý nào thì làm ý đó nha
1. Cho a,b,c là độ dài 3 cạnh tam giác. Chứng minh:
a) \(\frac{1}{\left(a+b-c\right)^2}+\frac{1}{\left(a-b+c\right)^2}+\frac{1}{\left(b+c-a\right)^2}\ge\frac{1}{a^2}+\frac{1}{b^2}+\frac{1}{c^2}\)
b) \(\frac{1}{\left(a+b-c\right)^3}+\frac{1}{\left(a-b+c\right)^3}+\frac{1}{\left(b+c-a\right)^3}\ge\frac{1}{a^3}+\frac{1}{b^3}+\frac{1}{c^3}\)
c) \(\frac{1}{\left(a+b-c\right)^{200}}+\frac{1}{\left(a-b+c\right)^{200}}+\frac{1}{\left(b+c-a\right)^{200}}\ge\frac{1}{a^{200}}+\frac{1}{b^{200}}+\frac{1}{c^{200}}\)
d) \(\frac{1}{8}\left(a+b\right)\left(b+c\right)\left(c+a\right)\ge\sqrt{abc\left(-a+b+c\right)\left(a-b+c\right)\left(a+b-c\right)}\)
e) \(a+b+c< \sqrt{a\left(b+c\right)}+\sqrt{b\left(a+c\right)}+\sqrt{c\left(a+b\right)}\)
f) \(\sqrt{\frac{a}{b+c}}+\sqrt{\frac{b}{c+a}}+\sqrt{\frac{c}{a+b}}< \sqrt{6}\)
g) \(\sqrt{-a+b+c}+\sqrt{a-b+c}+\sqrt{a+b-c}\le\sqrt{3\left(a+b+c\right)}\)
Cho 3 số a,b,c đôi 1 phân biệt.CMR:
\(\frac{b-c}{\left(a-b\right)\left(a-c\right)}+\frac{c-a}{\left(b-c\right)\left(b-a\right)}+\frac{a-b}{\left(c-a\right)\left(c-b\right)}=2\left(\frac{1}{a-b}+\frac{1}{b-c}+\frac{1}{c-a}\right)\)
\(VT=\frac{b-c}{\left(a-b\right)\left(a-c\right)}+\frac{c-a}{\left(b-c\right)\left(b-a\right)}+\frac{a-b}{\left(c-a\right)\left(c-b\right)}\)
\(=\frac{\left(b-a\right)-\left(c-a\right)}{\left(b-a\right)\left(c-a\right)}+\frac{\left(c-b\right)-\left(a-b\right)}{\left(c-b\right)\left(a-b\right)}+\frac{\left(a-c\right)-\left(b-c\right)}{\left(a-c\right)\left(b-c\right)}\)
\(=\frac{1}{c-a}-\frac{1}{b-a}+\frac{1}{a-b}-\frac{1}{c-b}+\frac{1}{b-c}-\frac{1}{a-c}\)
\(=\frac{1}{c-a}+\frac{1}{a-b}+\frac{1}{a-b}+\frac{1}{b-c}+\frac{1}{b-c}+\frac{1}{c-a}\)
\(=2\left(\frac{1}{a-b}+\frac{1}{b-c}+\frac{1}{c-a}\right)=VP\left(đpcm\right)\)
cho a b c la số dương, biết a+b+c<=3. Tìm Pmin
\(P=\frac{a^2}{\left[\sqrt{b^3+8}-\left(c-1\right)^2\right]}+\frac{b^2}{\left[\sqrt{c^3+8}-\left(a-1\right)^2\right]}+\frac{c^2}{\left[\sqrt{a^3+8}-\left(b-1\right)^2\right]}\)
cho a,b,c>0. Chứng minh rằng \(\left(a+\frac{1}{b}-1\right)\left(b+\frac{1}{c}-1\right)+\left(b+\frac{1}{c}-1\right)\left(c+\frac{1}{a}-1\right)+\left(c+\frac{1}{a}-1\right)\left(a+\frac{1}{b}-1\right)>=3\)