Giải thích các bước giải:
a.Ta có:
$\sqrt{7.28(x-1)^2}$
$=\sqrt{7.2^2.7(x-1)^2}$
$=\sqrt{2^2.7^2.(x-1)^2}$
$=\sqrt{(2.7.(x-1))^2}$
$=|2.7.(x-1)|$
$=|14(x-1)|$
$=14|x-1|$
$=14(1-x)$ vì $x<1\to x-1<0\to |x-1|=1-x$
f.Ta có:
$\sqrt{6.6.(3-x)^2}$
$=\sqrt{6^2.(3-x)^2}$
$=\sqrt{(6(3-x))^2}$
$=|6(3-x)|$
$=6|3-x|$
$=6(x-3)$ vì $x>3\to 3-x<0\to |3-x|=-(3-x)=x-3$
k.Ta có:
$\sqrt{49(3-3x)^2}$
$=\sqrt{7^2(3-3x)^2}$
$=\sqrt{(7(3-3x))^2}$
$=|7(3-3x)|$
$=21|1-x|$
$=21(x-1)$ vì $x\ge 1\to 1-x\le 0\to |1-x|=x-1$
