giải ptrinh: a. x-342/15 + x-323/17 + x-300/19 +x-272/21 =0 b. x+1/15 + x+2/7 + x+4/4 +7 = 0

Bạn tham khảo nhé

a)     $\frac{x-342}{15}$ + $\frac{x-323}{17}$ + $\frac{x-300}{19}$ + $\frac{x-272}{21}$ = 0 

<=> $\frac{2261(x-342)}{33915}$ + $\frac{1995(x – 323)}{33915}$ + $\frac{1785(x-300)}{33915}$ + $\frac{1615(x – 272)}{33915}$ = 0

   => 2261(x – 342) + 1995(x – 323) + 1785(x – 300) + 1615(x – 272) = 0 

<=> 2261x – 773262 + 1995x – 644385 + 1785x – 535500 + 1615x – 439280 = 0

<=> 7656x – 2392427 = 0

<=>                  7656x = 2392427

<=>                          x ≈ 312,49

Vậy x ≈ 312,49

b) $\frac{x+1}{15}$ + $\frac{x+2}{7}$ + $\frac{x+4}{4}$ + 7 = 0 

<=>$\frac{28(x+1)}{420}$ +$\frac{60(x+2)}{420}$ + $\frac{105(x+4)}{420}$ + $\frac{420.7}{420}$ = 0 

  => 28(x + 1) + 60(x + 2) + 105(x + 4) + 2940 = 0 

<=> 28x + 28 + 60x + 120 + 105x + 420 + 2940 = 0

<=> 193x + 3508 = 0 

<=> 193x = -3508

<=>       x = -$\frac{3508}{193}$

Vậy x = -$\frac{3508}{193}$