Xét \(∆ ABC\) có \(MN // BC\) (gt)
Theo hệ quả định lí Ta-lét ta có:
\(\displaystyle {{AN} \over {AB}} = {{AM} \over {AC}} = {{MN} \over {BC}}\)
\(\displaystyle \Rightarrow {{10} \over {25}} = {{16} \over y} = {x \over {45}}\)
\(\displaystyle \Rightarrow y = {{25.16} \over {10}} = 40\;(cm)\)
\(\displaystyle \Rightarrow x = {{10.45} \over {25}} = 18\;(cm)\)
