# giúp mik vsssssssssss

giúp mik vsssssssssss

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1. Đáp án:

bài 3:

a)102+2(x-3)=108

⇔2(x-3)=108-102

⇔2(x-3)=6

⇔x-3=3

⇔x=6

b) [(x^2+2)+17]:5=20

⇔x^2+2+17=20.5

⇔x^2+19=100

⇔x^2=100-19

⇔x^2=81

⇔x=+-9

c) (x-1)^4=81

Th1: (x-1)^4=3^4⇔x-1=3⇔x=4

Th2: (x-1)^4=(-3)^4⇔x-1=-3⇔x=-2

bài 4:

A=1+4+4^2+4^3+…+4^100

4A=4+4^2+4^3+…+4^101

4A-A=(4+4^2+…+4^101)-(1+4+4^2+…+4^100)

3A=4^101-1

A=(4^101-1)/3

khi đó:

B=(4^101-1)/3-A=(4^101-1)/3-(4^101-1)/3=0

vậy B=0

2. Euphemia

bài 3:

a) $102+2(x-3)=108$

$↔2(x-3)=108-102=6$

$↔x-3=6:2=3$

$↔x=3+3=6$

b) $[(x^2+2)+17]:5=20$

$↔(x^2+2)+17=20.5=100$

$↔x^2+2=100-17=83$

$↔x^2=83-2=81$

$$↔\left[ \begin{array}{l}x=9\\x=-9\end{array} \right.$$

c) $(x-1)^4=81$

$$↔\left[ \begin{array}{l}x-1=3\\x-1=-3\end{array} \right.$$ $\to$ $$\left[ \begin{array}{l}x=4\\x=-2\end{array} \right.$$

Bài 4:

$A=1+4+4^2+4^3+…+4^{100}$

$4A=4+4^2+4^3+…+4^{101}$

$4A-A=(4+4^2+4^3+…+4^{101})-(1+4+4^2+…+4^{100}$

$3A=4^{101}-1$

$→A=\dfrac{4^{101}-1}{3}$

$→B=(4^{101}-1):3-A=\dfrac{4^{101}-1}{3}-\dfrac{4^{101}-1}{3}=0$