Gọi ba cạnh là \(x;y;z\)
Theo đề bài :
\(\dfrac{x}{2}=\dfrac{y}{3}=\dfrac{z}{4}=x+y+z=45\)
Theo tính chất dãy tỉ số bằng nhau ta có :
\(\dfrac{x}{2}+\dfrac{z}{3}+\dfrac{y}{4}=\dfrac{x+y+z}{9}=\dfrac{45}{9}=5\)
\(\dfrac{x}{2}=5=x=5.2=10\left(cm\right)\)
\(\dfrac{y}{3}=5=y=5.3=15\left(cm\right)\)
\(\dfrac{z}{4}=5=z=5.4=20\left(cm\right)\)
Vậy chọn B
Gọi dộ dài 3 cạnh là a,b, c (cm)
Ta có:
\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{4}=\dfrac{a+b+c}{2+3+4}=\dfrac{45}{9}=5\\ \Rightarrow a=5.2=10\left(cm\right);b=5.3=15\left(cm\right);c=5.4=20\left(cm\right)\)
=> C
Gọi dộ dài 3 cạnh là a,b, c (cm)
Ta có:
\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{4}=\dfrac{a+b+c}{2+3+4}=\dfrac{45}{9}=5\\ \Rightarrow a=5.2=10\left(cm\right);b=5.3=15\left(cm\right);c=5.4=20\left(cm\right)\)
=> C
Gọi dộ dài 3 cạnh là a,b, c (cm)
Ta có:
\(\dfrac{a}{2}=\dfrac{b}{3}=\dfrac{c}{4}=\dfrac{a+b+c}{2+3+4}=\dfrac{45}{9}=5\\ \Rightarrow a=5.2=10\left(cm\right);b=5.3=15\left(cm\right);c=5.4=20\left(cm\right)\)
=> C