a, Rtđ = R1 + R2 + R3 = 10 + 20 +10 = 40 ôm

b, I1= 4/10 = 0,4A

I=I1 = I2 = I3 = 0,4 A

Uab= Rtđ. I = 40.0,4=16 V

-\(\dfrac{\sqrt{5}+\sqrt{3}}{2}\)

kia là phẩy hay nhân đấy bạn

a, <=> (2x-1)(2x-1-2x-3)=0

<=> (2x-1).-4=0

<=> -8x + 4= 0

<=> -8x=-4 <=> x= 1/2

= 1 x 512 : 8

= 64

= 8x³ - 40x² - 20x + 4x² 

= 8x³ - 36x² - 20x

= 8x³ + 4x² - 40x² -20x

= 4x².(2x + 1) - 20x.(2x+1)=(4x²-20x).(2x+1)

x=2

a, 3x² - 6x = 0

<=>x.(3x-6)=0

<=>x=0 ; 3x -6=0

<=>3x-6=0<=>3x=6<=>x=2;x=0

b

x2 -10x = -25

<=>x2 -10x +25 =0

<=>x2 - 5x - 5x +25 =0

<=>x.(x-5) -5.(x-5)=0 

<=>(x-5).(x-5)=0

<=>x-5=0   <=> x= 5