Giải câu 2 trang 63 sách toán VNEN lớp 8 tập 2.
Ta có:$\Delta $ A'B'C' $\sim $ $\Delta $ ABC nên
$\frac{A'B'}{AB}$ = $\frac{A'C'}{AC}$ = $\frac{B'C'}{BC}$
a)
Ta có: A'B' = AB + 10,8 = 26,1 cm
$\frac{A'C'}{AC}$ = $\frac{B'C'}{BC}$ = $\frac{A'B'}{AB}$ = $\frac{26,1}{15,3}$
$\rightarrow $ A'C' = $\frac{26,1}{15,3}$ . AC = $\frac{26,1}{15,3}$ . 31,2 $\approx $ 53,22 cm
B'C' = $\frac{26,1}{15,3}$ . BC = $\frac{26,1}{15,3}$ . 21,3 $\approx $ 36,34 cm
b)
Ta có: A'B' = AB - 5,4 = 9,9 cm
$\frac{A'C'}{AC}$ = $\frac{B'C'}{BC}$ = $\frac{A'B'}{AB}$ = $\frac{9,9}{15,3}$
$\rightarrow $ A'C' = $\frac{9,9}{15,3}$ . AC = $\frac{9,9}{15,3}$ . 31,2 $\approx $ 20,19 cm
B'C' = $\frac{9,9}{15,3}$ . BC = $\frac{9,9}{15,3}$ . 21,3 $\approx $ 13,78 cm