Question

calcular o valor de x nas proporções
x/7=9/21
x-2/12=x/20
x/10=7/5
3/15=x/5
12/3=8/x
x/4=2/7

Answer 1

Calcular o valor de x nas proporções

FRAÇÃO = FRAÇÃO ( só cruzar)


 

x/7=9/21

x     9
--- = ----
7     21

21(x) =7(9) 
21x = 63
x = 63/21
x = 3


x-2/12=x/20

x - 2     x
----- = ------
12       20

12(x) =   20(x - 2) 
12x = 20x - 40
12x - 20x = -40
- 8x = - 40
x = - 40/-8
x = + 40/8
x = 5

x/10=7/5


x        7
--- = ------
10      5

5(x) = 10(7)
5x = 70
x = 70/5
x = 14

3/15=x/5

3        x
--- = ----
15      5

15(x) = 3(5)
15x = 15
x = 15/15
x = 1

12/3=8/x

12         8
----- = ------
 3           x

12(x) = 3(8)
12x  = 24
x = 24/12
x = 2

x/4=2/7

x        2
--- = ----
4       7

7(x) = 4(2)
7x = 8
x = 8/7

Answer 2

x  =  9   ==> 21x = .79 ==> 21x = 63 ==> x = 3
7     21
=============================================
x-2 = x ==> 20x - 40 = 12x ==> 20x-12x= 40 ==> 8x = 40 ==> x=5
 12   20
======================================================
  x = 7 ==> 5x = 70 ==> x = 14
10   5
=================================================
  3 = x  ==> 15x = 15 ==> x = 1
15    5
==================================================
12 = 8  ==> 12x = 24 ==> x = 2
 3     x
====================================================
x = 2  ==> 7x = 8 ==> x = 8/7
4    7