3^x-2+3^x=90 x=?
Cho cos x =2/3 và 0<x<90. Tính cos(90-x) và cot x
\(0< x< 90^0\)
=>\(sinx>0\)
\(sin^2x+cos^2x=1\)
=>\(sin^2x=1-\dfrac{4}{9}=\dfrac{5}{9}\)
=>\(sinx=\dfrac{\sqrt{5}}{3}\)
\(cos\left(90-x\right)=sinx=\dfrac{\sqrt{5}}{3}\)
\(cotx=\dfrac{cosx}{sinx}=\dfrac{2}{3}:\dfrac{\sqrt{5}}{3}=\dfrac{2}{\sqrt{5}}\)
S=1 x 2 x 3 + 2 x 3 x 4 + 3 x 4 x 5 +.... + 88 x 89 x 90
c = 1 x 2 + 2 x 3 + 3 x 4 + 4 x 5 + ... + 90 x 100
Mk trả lời đc nè nguyen hung son :))
A = 1 . 2 + 2 . 3 + 3 . 4 + 4 . 5 + ... + 90 . 100
3A = 1 . 2 . 3 + 2 . 3 . ( 4 - 1 ) + 3 . 4 . ( 5 - 2 ) + .... + 90 . 100 . ( 101 - 98 )
3A = 1 . 2 . 3 + 2 . 3 . 4 - 1 + 3 . 4 . 5 - 2 + ... + 90 . 100 . 101 - 98
3A = 99 . 100 . 101
A = ( 99 . 100 . 101 ) : 3
A = 999900 : 3
A = 333300
Vậy A = 333300
minh dang ding tra loi the dau tay a
duong k cho ban ay luon di
(x + 1) + (x + 2) + (x + 3) +.... + (x + 90) = 4248
\(\Leftrightarrow90x+\left(1+2+3+...+90\right)=4248\)
\(\Leftrightarrow90x+\dfrac{\left(90+1\right).90}{2}=4248\)
\(\Leftrightarrow90x+4095=4248\)
\(\Leftrightarrow90x=4248-4095=153\)
\(\Leftrightarrow x=\dfrac{153}{90}\)
3^x+3^x+2=90
3^x+3^x+2=90
=> 2.3x=90-2
=> 2.3x=88
=> 3x=88:2
=> 3x=44
=> ?? đề sai hả?
lần sau bạn ghi rõ ra nha kẻo người ta nhầm :33
3^x + 3^x+2 = 90
3^x + 3^x . 3^2 = 90
3^x . 1 + 3^x . 9 = 90
3^x (1+9) = 90
3^x . 10 = 90
3^x = 90 : 10 = 9
=> x = 2
3^x-2+3^x=90
3^x-2+3^x=90
\(3^{x-2}+3^x=90\)
\(\Leftrightarrow\frac{3^x}{9}+3^x=90\)
\(\Leftrightarrow3^x\left(\frac{1}{9}+1\right)=90\)
\(\Leftrightarrow3^x=81\)
\(\Leftrightarrow x=4\)
3\(^x\)- 2 + 3\(^x\)=90
2.3\(^x\)- 2 =90
2.3\(^x\) =92
3\(^x\) =46
x =\(\sqrt[3]{46}\)
Ta có 3^(x-2) + 3^x =90
=> 3^x .1/(3^2) +3^x =90
=> 3^x ( 1/9 +1) =90
=> 3^x .10/9 =90
=> 3^x =81 => 3^x =3^4
=> x=4
Vậy x=4
Tìm x € Z , biết :
a) 14 - (40 - x) = -27
b) 2 (5 - x) - 7 (x - 2) = -3
c) (x : 3) + 2^3 ) . 3^2 = -90
3x+2+3x=90
1+2+3+...+x=210
a, 3x+2 +3x = 90
3x . 32 + 3x = 90
3x. ( 32 + 1 ) = 90
3x . 10 =90
3x = 90 : 10
3x = 9
3x = 32
x = 2
1+2+3+......+x =210
(x+1) . x : 2= 210
(x+1) . x = 210 .2
(x+1) .x = 420
21 . 20 = 420
x = 20