\(\text{Vì tứ giác có chu vi bằng 76 cm nên a + b + c + d = 76}\\ \text{Áp dụng tính chất dãy tỉ số bằng nhau ta có:}\\ \dfrac{a}{2}=\dfrac{b}{5}=\dfrac{c}{4}=\dfrac{d}{7}=\dfrac{a+b+c+d}{2+5+4+7}=\dfrac{76}{18}=\dfrac{38}{9}\\ ⇒a=\dfrac{38}{9}\times 2=\dfrac{76}{9}\ (cm)\\ b=\dfrac{38}{9}\times 5=\dfrac{190}{9}\ (cm)\\ c=\dfrac{38}{9}\times 4=\dfrac{152}{9}\ (cm)\\ d=\dfrac{38}{9}\times 7=\dfrac{266}{9}\ (cm)\)
Đáp án:
\(a=\dfrac{38}{9}\times 2=\dfrac{76}{9}\ (cm)\\ b=\dfrac{38}{9}\times 5=\dfrac{190}{9}\ (cm)\\ c=\dfrac{38}{9}\times 4=\dfrac{152}{9}\ (cm)\\ d=\dfrac{38}{9}\times 7=\dfrac{266}{9}\ (cm)\)
Giải thích các bước giải:
\(\text{Vì tứ giác có chu vi bằng 76 cm nên a + b + c + d = 76}\\ \text{Áp dụng tính chất dãy tỉ số bằng nhau ta có:}\\ \dfrac{a}{2}=\dfrac{b}{5}=\dfrac{c}{4}=\dfrac{d}{7}=\dfrac{a+b+c+d}{2+5+4+7}=\dfrac{76}{18}=\dfrac{38}{9}\\ ⇒a=\dfrac{38}{9}\times 2=\dfrac{76}{9}\ (cm)\\ b=\dfrac{38}{9}\times 5=\dfrac{190}{9}\ (cm)\\ c=\dfrac{38}{9}\times 4=\dfrac{152}{9}\ (cm)\\ d=\dfrac{38}{9}\times 7=\dfrac{266}{9}\ (cm)\)
chúc bạn học tốt!
$a:b:c:d=2:5:4:7$
$→ \dfrac{a}{2}=\dfrac{b}{5}=\dfrac{c}{4}=\dfrac{d}{7}$
$= \dfrac{a+b+c+d}{2+5+4+7}=\dfrac{76}{18}=\dfrac{38}{9}$
$→ a=\dfrac{38}{9}.2=\dfrac{76}{9}$ (cm)
$b=\dfrac{38}{9}.5=\dfrac{190}{9}$ (cm)
$c=\dfrac{38}{9}.4=\dfrac{152}{9}$ (cm)
$d=\dfrac{38}{9}.7=\dfrac{266}{9}$ (cm)