15 x15 =225
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( 123 x 345 ) x ( 13 x 15 - 12 x 15 - 15 )
= ( 123 x 345 ) x ( 13 x 15 - 12 x 15 - 15 x 1 )
= ( 123 x 345 ) x ( (13 - 12 -1 ) x 15 )
= ( 123 x 345 ) x ( 0 x 15 )
= ( 123 x 345 ) x 0
= 0
![](https://rs.olm.vn/images/avt/0.png?1311)
558 - (15 : x + 29) x 17 = 14
\(\Rightarrow\left(15:x+29\right)\times17=558-14\)
\(\Rightarrow\left(15:x+29\right)\times17=544\)
\(\Rightarrow15:x+29=544:17\)
\(\Rightarrow15:x+29=32\)
\(\Rightarrow15:x=32-29\)
\(\Rightarrow15:x=3\)
\(\Rightarrow x=15:3\)
\(\Rightarrow x=5\)
Vậy x = 5
\(\left(x+40\right)\times15=75\times24\)
\(\Rightarrow\left(x+40\right)\times15=1800\)
\(\Rightarrow x+40=1800:15\)
\(\Rightarrow x+40=120\)
\(\Rightarrow x=120-40\)
\(\Rightarrow x=80\)
Vậy x = 80
![](https://rs.olm.vn/images/avt/0.png?1311)
Vì x=14 nên x+1=15
Thay 15=x+1 vào A(x) Ta có:
A(x)= x^15-(x+1)x^14+(x+1)x^13-(x+1)x^12+...+(x+1)x^3-(X+1)^2+(x+1)x-15
=x^15-x^15-x^14+x^14+x^13-x^13-...+X^4+x^3-X^3-x^2+x^2-x-15
=x-15
=> A(14)=14-15=-1
Vậy A(14)=-1
k mình nha
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3n.152=3n.(3.5)2=3n.32.52=3n+2.52
=>(n+2+1).(2+1)=15
(n+2+1).3=15
n+2+1=15:3
n+2+1=5
n+2=5-1
n+2=4
n=4-2
n=2
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 2x . 4 = 128
<=> 2x = 32
<=> 2x = 25
<=> x = 5
b) x15 = x1
<=> x15 - x = 0
<=> x(x14 - 1) = 0
<=> \(\orbr{\begin{cases}x=0\\x^{14}-1=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=0\\x^{14}=1^{14}\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=0\\x=\pm1\end{cases}}\)
c) (2x + 1)3 = 125
<=> (2x + 1)3 = 53
<=> 2x + 1 = 5
<=> 2x = 4
<=> x = 2
d) (x - 5)4 = (x - 5)6
<=> (x - 5)6 - (x - 5)4 = 0
<=> (x - 5)4[(x - 5)2 - 1] = 0
<=> \(\orbr{\begin{cases}\left(x-5\right)^4=0\\\left(x-5\right)^2-1=0\end{cases}}\)
Khi (x - 5)4 = 0 => x - 5 = 0 => x = 5
Khi (x - 5)2 - 1 = 0 <=> (x - 5)2 = 12 <=> \(\orbr{\begin{cases}x-5=1\\x-5=-1\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=6\\x=4\end{cases}}\)
17 x17 =289