Đáp án:
Giải thích các bước giải:
$a)( X+1)+(X+4)+(X+7)+(X+10)+…+(X+28)=155$
$x+ 1+ x+ 4+ x+ 7+ x+ 10+...+ x+ 28= 155$
$(x+ x+ x+ x+...+ x)+ (1+ 4+ 7+ 10+...+ 28)= 155$
$[(28- 1): 3+ 1= 10 (x)+ (28+ 1). 10: 2= 145]$
$x. 10+ 145= 155$
$x. 10= 155- 145$
$x. 10= 10$
$c= 10: 10= 1$
$b)53,2:(X_3,5)+46,8=99$
$53, 2: (x- 3,5)= 53,2$
$x- 3,5= 1$
$= 1+ 3,5= 4,5$
$c)71+65×4=X+140/X+260$
$x+ \dfrac{140}{x}+ 260= 71+ 65. 4$
$x+ \dfrac{140}{x}+ 260= 71+ 260$
$x+ \dfrac{140}{x}= 71$
$\dfrac{x}{x}+ \dfrac{140}{x}= 71$
$1+ x+ \dfrac{140}{x}= 71$
$\dfrac{140}{x}= 71- 1$
$\dfrac{140}{x}= 70$
$x= \dfrac{140}{70}$
$x= 2$
