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\(A=\left(\frac{a+b}{b}\right).\left(\frac{b+c}{c}\right).\left(\frac{a+c}{a}\right)\)
Vì \(a+b+c=0\)
\(\Rightarrow\hept{\begin{cases}a+b=-c\\b+c=-a\\a+c=-b\end{cases}}\)
\(\Rightarrow A=\frac{-c}{b}.\left(\frac{-a}{c}\right).\left(\frac{-b}{a}\right)\)
\(\Rightarrow A=-1\)
\(\frac{b+c-a}{a}+\frac{2a}{a}=\frac{a+c-b}{b}+\frac{2b}{b}=\frac{a+b-c}{c}+\frac{2c}{c}\)
\(\frac{a+b+c}{a}=\frac{a+b+c}{b}=\frac{a+b+c}{c}\)
=> a=b=c
A=(1+1)(1+1)(1+1) = 2.2.2 =8
=>\(\frac{a-b+c}{2b}+1=\frac{c-a+b}{2a}+1=\frac{a-c+b}{2c}+1\)
\(\Rightarrow\frac{a+b+c}{2b}=\frac{a+b+c}{2a}=\frac{a+b+c}{2c}\)
*TH1: nếu a+b+c=0 => a+b=-c; b+c=-a; c+a=-b
=>P=\(\left(\frac{b+c}{b}\right)\left(\frac{a+b}{a}\right)\left(\frac{c+a}{c}\right)\)
=\(\frac{-a}{b}.\frac{-c}{a}.\frac{-b}{c}=\frac{-\left(a.b.c\right)}{a.b.c}=-1\)
*TH2: Nếu a+b+c khác 0: thì a=b=c
Khi đó P=2.2.2=8
Vậy P= -1 hoặc 8
\(\frac{a-b+c}{2b}=\frac{c-a+b}{2a}=\frac{a-c+b}{2c}=\frac{a+b+c}{2\left(a+b+c\right)}=\frac{1}{2}\)
=> 2a-2b+2c=2b <=> a+c=2b. Chia cả 2 vế cho c ta được: \(1+\frac{a}{c}=\frac{2b}{c}\)
Tương tự: \(1+\frac{c}{b}=\frac{2a}{b}\) và \(1+\frac{b}{a}=\frac{2c}{a}\)
=> \(\left(1+\frac{c}{b}\right)\left(1+\frac{b}{a}\right)\left(1+\frac{a}{c}\right)=\frac{2a}{b}.\frac{2c}{a}.\frac{2b}{c}=\frac{8.abc}{abc}=8\)
Đáp số: 8
\(\frac{a+b}{c}=\frac{b+c}{a}=\frac{a+c}{b}\)
<=> \(\frac{a+b}{c}+1=\frac{b+c}{a}+1=\frac{a+c}{b}+1\)
<=> \(\frac{a+b+c}{c}=\frac{a+b+c}{a}=\frac{a+b+c}{b}\)
<=> a + b + c = 0 hoặc a = b = c.
Th1: a + b + c = 0
=> a + b = - c ; a + c = -b ; b + c = -a.
Thế vào P :
\(P=\left(1+\frac{a}{b}\right)\cdot\left(1+\frac{b}{c}\right)\cdot\left(1+\frac{c}{a}\right)\)
\(=\left(\frac{a+b}{b}\right)\cdot\left(\frac{b+c}{c}\right)\cdot\left(\frac{c+a}{a}\right)\)
\(=-\frac{c}{b}.\frac{\left(-a\right)}{c}.\frac{\left(-b\right)}{a}=-1\)
TH2: a = b = c. THế vào P
\(P=\left(1+1\right).\left(1+1\right).\left(1+1\right)=8\)
Vậy: P = -1 nếu a + b + c = 0
hoặc P = 8 nếu a = b = c.
\(P=\left(1+\frac{a}{b}\right)\left(1+\frac{b}{c}\right)\left(1+\frac{c}{a}\right)=\frac{a+b}{b}.\frac{b+c}{c}.\frac{c+a}{a}\)
Ta có: \(\frac{a+b}{c}=\frac{b+c}{a}=\frac{a+c}{b}\)\(\Rightarrow\frac{a+b}{c}+1=\frac{b+c}{a}+1=\frac{a+c}{b}+1=\frac{a+b+c}{c}=\frac{a+b+c}{a}=\frac{a+b+c}{b}\)
TH1: Nếu \(a+b+c=0\)\(\Rightarrow\hept{\begin{cases}a+b=-c\\b+c=-a\\c+a=-b\end{cases}}\)
\(\Rightarrow P=\frac{-c}{b}.\frac{-a}{c}.\frac{-b}{a}=\frac{\left(-a\right).\left(-b\right).\left(-c\right)}{abc}=-1\)
TH2: Nếu \(a+b+c\ne0\)\(\Rightarrow a=b=c\)
\(\Rightarrow\hept{\begin{cases}a+b=2b\\b+c=2c\\c+a=2a\end{cases}}\)\(\Rightarrow P=\frac{2b}{b}.\frac{2c}{c}.\frac{2a}{a}=2.2.2=8\)
Vậy \(P=-1\)hoặc \(P=8\)
Câu hỏi của vũ ngọc vân - Toán lớp 7 - Học toán với OnlineMath
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Ta có: a+b+c=0a+b+c=0
\Rightarrow b+a=-c⇒b+a=−c
\Rightarrow c+b=-a⇒c+b=−a
\Rightarrow a+c=-b⇒a+c=−b
Ta có: A=\left(1+\frac{a}{b}\right)\left(1+\frac{b}{c}\right)\left(1+\frac{c}{a}\right)A=(1+
b
a
)(1+
c
b
)(1+
a
c
)
\Rightarrow A=\left(\frac{b+a}{b}\right)\left(\frac{c+b}{c}\right)\left(\frac{a+c}{a}\right)⇒A=(
b
b+a
)(
c
c+b
)(
a
a+c
)
\Rightarrow A=\left(\frac{-c}{b}\right)\left(\frac{-a}{c}\right)\left(\frac{-b}{a}\right)⇒A=(
b
−c
)(
c
−a
)(
a
−b
)
\Rightarrow A=-1⇒A=−1
ddap an la bang -1