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1/h=1/2(1/a+1/b)=1/2a+1/2b=(a+b)/2ab
=>(a+b/)2ab-1/h=0
quy dong len ta co
(a+b)h/2abh-2ab/2abh=0=> (ah+bh-2ab)/2abh=0 =>ah+bh-2ab=0
=>ah+bh-ab-ab=0
=>a(h-b)-b(a-h)=0
=>a(h-b)=b(a-h)
=>a/b=(a-h)(h-b)
87 - 218 = (23)7 - 218
= 221 - 218
= 217.(24 - 2)
= 217.14 chia hết cho 14 (đpcm)
1: so sánh 2016/2017+2017/2018
vì 2016/2017 > 1/2017 >1/2018 =
> 2016/2017+2017/2018 >1/2018+2017/2018=1
vậy .....
ta co : 3n+2 /n -1
=(3n - 3 + 5)/ (n-1)
=3(n-1) + 5 / (n-1)
=3(n-1)/ (n-1) + 5/(n-1)
=3 + 5/(n-1)
De 3n+2 chia het cho n-1
<=>n-1 thuộc Ư(5)={+-1;+-5}
=>n={2;0;6;-4}
bạn an ơi vì sao (3n-3+5) khi bỏ dấu ngoặc ra lại bàng 3(n-1) +5 vậy?
a) \(\left(x+\frac{1}{3}\right)^3=\frac{-8}{27}\)
\(\left(x+\frac{1}{3}\right)^3=\left(\frac{-2}{3}\right)^3\)
\(x+\frac{1}{3}=\frac{-2}{3}\)
\(x=-1\)
b) \(\left(\frac{1}{3}x+\frac{4}{3}\right)^2=\frac{25}{9}\)
\(\left(\frac{1}{3}x+\frac{4}{3}\right)^2=\left(\frac{5}{3}\right)^2\)
\(\frac{1}{3}x+\frac{4}{3}=\frac{5}{3}\)
\(\frac{1}{3}x=\frac{1}{3}\)
\(x=1\)
c) \(2^x+2^{x+1}=24\)
\(2^x+2^x.2=24\)
\(2^x.\left(1+2\right)=24\)
\(2^x.3=24\)
\(2^x=8\)
\(2^x=2^3\)
\(x=3\)
a, (x+1/3)^3 = -8/27
=>(x+1/3)^3 = (-2/3)^3
=>x+1/3 = -2/3
=>x = -1
b, (1/3x+4/3)^2 = 25/9
=>(1/3x+4/3)^2 = (5/3)^2
=>(1/3x+4/3) = 5/3
=>1/3x = 1/3
=> x = 1
c, 2^x + 2^x+1 = 24
=>2^x + 2^x . 2 = 24
=>2^x.(1+2) = 24
=>2^x . 3 = 24
=>2^x =8
=>2^x = 2^3
=> x = 3
Ta có :
\(C=\frac{2-1}{2!}+\frac{3-1}{3!}+\frac{4-1}{4!}+...+\frac{n-1}{n!}\)
\(=\left(\frac{2}{2!}+\frac{3}{3!}+\frac{4}{4!}+...+\frac{n}{n!}\right)-\left(\frac{1}{2!}+\frac{1}{3!}+\frac{1}{4!}+...+\frac{1}{n!}\right)\)
\(=\left(1+\frac{1}{2!}+\frac{1}{3!}+....+\frac{1}{\left(n-1\right)!}\right)-\left(\frac{1}{2!}+\frac{1}{3!}+\frac{1}{4!}+....+\frac{1}{n!}\right)\)
\(=1+\frac{1}{2!}+\frac{1}{3!}+....+\frac{1}{\left(n-1\right)!}-\frac{1}{2!}-\frac{1}{3!}-\frac{1}{4!}-....-\frac{1}{n!}\)
\(=1-\frac{1}{n!}=\frac{n!-1}{n!}\)
Đặt A=1+2+22+..............+22017
\(\Rightarrow\)2A =2+22+23+.............+22018
\(\Rightarrow\)2A -A = (2+22+23+............+22018) -(1+2+22 +...............+22017)
\(\Rightarrow\)A= 22018 -1
Lại có :A = ( 23 )672 .22 -1 =(7+1)672 .22 -1= ( B(7) +1).22 -1 =22 .B(7) +22-1=22 .B(7)+3
Vây A chia 7 dư 3