Giải bài 6 trang 47

Đề bài

a) $\sqrt{{74}^2-{70}^2}$

b) $\sqrt{{\left(62,5{)}^2-(58,5\right)}^2}+\left(\sqrt{11}-2\sqrt{5}\right)\left(\sqrt{11}+2\sqrt{5}\right)$

Lời giải chi tiết

a) $\sqrt{{74}^2-{70}^2}$

$=\sqrt{\left(74+70\right)\left(74-70\right)}=\sqrt{144.4}=\sqrt{{12}^2}.\sqrt{2^2}$

$=12.2=24$.

b) $\sqrt{\left(62,5+58,5\left)\right(62,5-58,5\right)}+{\left(\sqrt{11}\right)}^2-{\left(2\sqrt{5}\right)}^2$

$=\sqrt{121.4}+11-4.5=\sqrt{{11}^2}.\sqrt{2^2}-9$

$=11.2-9=13.$