1.
a) $\sqrt[]{25}$ + $\sqrt[]{2,25}$ = 5 + 1,5 = 6,5
b) $\sqrt[]{0,81}$ - $\sqrt[]{0,04}$ = 0,9 + 0,2 = 1,1
2.
a) 4 - $2\sqrt[]{3}$
b) 14 - $6\sqrt[]{5}$
c) x + $6\sqrt[]{x}$ + 9
3.
a) = 15 000x
b) 140 ngày
4.
$\frac{3}{x-3}$-$\frac{2}{x+3}$=$\frac{7x+1}{9-x^{2}}$
⇔ $\frac{3}{x-3}$-$\frac{2}{x+3}$=$\frac{-7x-1}{x^{2}-9}$
⇔ $\frac{3}{x-3}$-$\frac{2}{x+3}$=$\frac{-7x-1}{(x-3)(x+3)}$
⇔ $\frac{3(x+3)}{(x-3)(x+3)}$-$\frac{2(x-3)}{(x+3)(x-3)}$=$\frac{-7x-1}{(x-3)(x+3)}$
⇒ 3(x+3)-2(x-3)=-7x-1
⇔ 3x+9-2x+6+7x+1=0
⇔ 8x+16=0
⇔ x+2=0
⇔ x=-2
Vậy PT có TN là S={2}
Xin hay nhất ạ!!!
