Question

[phan khánh huyền]

Bài 1: Tìm x 
N biết.

a) (x -15).15 = 0
b) 32. (x -10) = 32
c) (x - 15) - 75 = 0
d) 575 - (6x +70) = 445
e) 315+ (125 - x) = 435
g) x -105 : 21 = 15
h) 231 - (x - 6) = 1339 : 13
i) 70 - 5(x - 3) = 45
k) 13 - 2(x + 1) = 7
i) 420 + 65.4 =(x+ 175) : 5 + 30
l) 32. 15 : 2 = ( x+ 70) : 14 - 40
m) 165 - (35: x + 3).19 = 13
n) 1+2+ 3 + 4 + 5 + .... + x = 528
p) (2x - 1) + (4x - 2) +... + (400x - 200) = 5 + 10 + ... + 1000

Answer 1

[Nguyễn Lê Phước Thịnh]

a: \(15\left(x-15\right)=0\)

mà 15>0

nên x-15=0

=>x=15

c: (x-15)-75=0

=>x-15=75

=>x=75+15=90

b: 32(x-10)=32

=>x-10=1

=>x=10+1=11

d: 575-(6x+70)=445

=>6x+70=575-445=130

=>6x=60

=>x=10

e: 315+(125-x)=435

=>440-x=435

=>x=440-435=5

g: x-105:21=15

=>x-5=15

=>x=15+5=20

h: \(231-\left(x-6\right)=1339:13\)

=>231-(x-6)=103

=>x-6=231-103=128

=>x=128+6=134

i: 70-5(x-3)=45

=>5(x-3)=70-45=25

=>x-3=5

=>x=5+3=8

k: 13-2(x+1)=7

=>2(x+1)=13-7=6

=>x+1=3

=>x=2

i: \(420+65\cdot4=\left(x+175\right):5+30\)

=>\(\dfrac{x+175}{5}=390+65\cdot4=390+260=650\)

=>x+175=3250

=>x=3250-175=3075

l: \(32\cdot15:2=\left(x+70\right):14-40\)

=>\(\left(x+70\right):14-40=16\cdot15=240\)

=>\(\left(x+70\right):14=240+40=280\)

=>\(x+70=14\cdot280=3920\)

=>x=3920-70=3850

m: \(165-\left(35:x+3\right)\cdot19=13\)

=>\(\left(35:x+3\right)\cdot19=165-13=152\)

=>35:x+3=152:19=8

=>35:x=8-3=5

=>x=35:5=7

n: \(1+2+3+4+...+x=528\)

=>\(\dfrac{x\left(x+1\right)}{2}=528\)

=>\(x\left(x+1\right)=528\cdot2=1056\)

=>\(x^2+x-1056=0\)

=>(x-32)(x+31)=0

=>\(\left[{}\begin{matrix}x=32\left(nhận\right)\\x=-31\left(loại\right)\end{matrix}\right.\)

p: \(\left(2x-1\right)+\left(4x-2\right)+...+\left(400x-200\right)=5+10+...+1000\)

=>\(\left(2x-1\right)\left(1+2+...+200\right)=5\left(1+2+...+200\right)\)

=>2x-1=5

=>2x=6

=>x=3