Question

Answer 1

Ta có: PR=PN+NR=8(cm)

Trong \(\Delta PQR\) có MN//QR(gt)

=> \(\dfrac{PM}{PQ}=\dfrac{PN}{PR}=>PQ=\dfrac{PM\cdot PR}{PN}=\dfrac{4\cdot8}{5}=6.4\left(cm\right)\)

Vậy PQ=6.4(cm)

Answer 2

Xét ΔPQR có 

M\(\in\)PQ(gt)

N\(\in\)PR(gt)

MN//QR(gt)

Do đó: \(\dfrac{PM}{PQ}=\dfrac{PN}{PR}\)(Định lí Ta lét)

\(\Leftrightarrow\dfrac{4}{PQ}=\dfrac{5}{8}\)

\(\Leftrightarrow PQ=\dfrac{4\cdot8}{5}=\dfrac{32}{5}=6,4\left(cm\right)\)

Vậy: PQ=6,4cm