Giải thích các bước giải:
B1:
a) 1/5 +5/7 : 15/14 -1,5
=1/5+2/3 -1,5
= 1/5+2/3 -3/2
=1/5+(2/3+3/2)
=1/5+13/6
= 71/30
b)
7 11/6 -(3 5/9 -2 7/6)+6 5/9
=7 11/6 -3 5/9 +2 7/6+6 5/9
=(7 11/6 +2 7/6) +(-3 5/9 +6 5/9)
=12+ 3
=15
c)
(-3/2)²-|-2/15|.25/4 +35%
=9/4-2/15.25/4 +7/20
=9/4-5/6+7/20
=(9/4-5/6)+7/20
=17/12+7/20
=53/30
d)
(-1/2)²: 3/4 -50%.(-2 1/2)-|-0,45|
=1/4 . 4/3 - 1/2.-5/2-9/20
=1/3+5/4-9/20
=17/15
B2:
a)
x-2,5=3 3/10
x-5/2=33/10
x=33/10+5/2
x=29/5
b)
3 1/4.x -2/5=1/4x+3/10
13/4.x-2/5=1/4.x+3/10
13/4x-1/4x=3/10+2/5
x(13/4-1/4)=7/10
x.3=7/10
x=7/10 :3
x=7/30
c)
-27/x+5 =x+5/-3
⇒-27. -3=(x+5).(x+5)
⇒81=(x+5)²
⇒9²=(x+5)²
⇒9=x+5
⇒x=9-5
⇒x=4
Vậy x=4
d)
1-3|2x- 1/3|=25%
1-3|2x- 1/3|= 1/4
3|2x-1/3|=1-1/4
3|2x-1/3|= 3/4
|2x- 1/3|=3/4 :3
|2x- 1/3|=1/4
TH1:
2x -1/3=1/4
2x=1/4+1/3
2x= 7/12
x=7/12 :2
x= 7/24
TH2:
2x -1/3=-1/4
2x=-1/4+1/3
2x= 1/12
x=1/12 :2
x=1/24
