giúp mik vsssssssssss Question giúp mik vsssssssssss in progress 0 Môn Toán RI SƠ 4 years 2020-10-14T02:16:50+00:00 2020-10-14T02:16:50+00:00 2 Answers 95 views 0
Answers ( )
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`
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:
$A=1+4+4^2+4^3+…+4^{100}$
$4A=4+4^2+4^3+…+4^{101}$
$4A-A=(4+4^2+4^3+…+4^{101})-(1+4+4^2+…+4^{100}$
$3A=4^{101}-1$
$→A=\dfrac{4^{101}-1}{3}$
$→B=(4^{101}-1):3-A=\dfrac{4^{101}-1}{3}-\dfrac{4^{101}-1}{3}=0$