Question

bài 1 / tìm x, biết

a/ 440 + 2 [ 125 - x ] = 546

b/ 7x - 3³ = 2⁷ chia 2⁴

c/ [ 12x - 4³ ] . 8³ = 4.8⁴

d/ 123 - 5.[ x + 4 ] = 38

e/ [ 2600 +6400 ] - 3.x = 1200

f/ x² - 72 chia 36 = 23

Answer 1

a/ 440 + 2 [ 125 - x ] = 546 

==> 2 [ 125 - x ] = 546 - 440 

==> 2 [ 125 - x ] 106 

==> 125 - x = 106 : 2 

==> 125 - x = 53  ==> x = 125 - 53 =72 

b/ 7x - 3³ = 2⁷ : 2⁴ 

==> 7x - 27 = 2^7-4 = 2³ = 8 

==> 7x = 8+ 27 

==> 7x = 35  ==> x = 35 : 7 = 5

c/  [ 12x - 4³ ] . 8³ = 4 . 8⁴ 

==> [ 12x - 2⁶ ] . 2⁹ = 2² . 2¹² 

==> [ 12x - 2⁶ ] . 2⁹ = 2¹⁴ 

==> [ 12x - 2⁶ ] = 2¹⁴ : 2⁹ = 2⁵ 

==>. 12x = 2⁵ + 2⁶ = 96 

==> x = 96 : 12 = 8

d/ 123 - 5. [ x + 4 ] = 38 

==> 5. [ x + 4 ] = 123 - 38 

==> 5. [ x + 4 ] = 85 

==> x + 4 = 85 : 5

==> x + 4 = 17 

==> x = 17 - 4 = 13 

e/ [ 2600 + 6400 ] - 3.x = 1200

==> 9000 - 3x = 1200

==> 3x = 9000 -1200 = 7800 

==> x = 7800 : 3 = 2600

f/ x² - 72 : 36 = 23 

==> x² - 2 = 23 

==> x² = 23 + 2 

==>x² = 25 

==> x² = 5² 

==> x = 5