Giải thích các bước giải:
$\dfrac{x-15}{21}+\dfrac{x-17}{23}+\dfrac{x-19}{25}+\dfrac{x-21}{27}=-4$
⇔ $\dfrac{x-15}{21}+1+\dfrac{x-17}{23}+1+\dfrac{x-19}{25}+1+\dfrac{x-21}{27}+1=0$
⇔ $\dfrac{x-15+21}{21}+\dfrac{x-17+23}{23}+\dfrac{x-19+25}{25}+\dfrac{x-21+27}{27}=0$
⇔ $\dfrac{x+6}{21}+\dfrac{x+6}{23}+\dfrac{x+6}{25}+\dfrac{x+6}{27}=0$
⇔ $(x+6)(\dfrac{1}{21}+\dfrac{1}{23}+\dfrac{1}{25}+\dfrac{1}{27})=0$
Vì $\dfrac{1}{21}+\dfrac{1}{23}+\dfrac{1}{25}+\dfrac{1}{27}) > 0$
nên $x+6=0$
⇔ $x=-6$
Chúc bạn học tốt !!!
