Root 9x

Algebra Level 1

9 × x = 81 , x = ? \large{\sqrt{\color{#cc0033}9 \color{#624F41}\times \color{#3D99F6}x } = \color{#20A900}{81}}, \ \ \ \ \ x= \ ?

1 0 729 9 81

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12 solutions

9 × x = 81 \sqrt{9 \times x} = 81 9 × x = 8 1 2 9 \times x = 81^2 x = 81 × 81 9 x=\frac{81 \times 81}{9} x = 729 x = \boxed{729}

Lew Sterling Jr
Apr 21, 2015

This was the easiest problem I could post and still only 60 % people could solve it . !!!! Amazing !!!!!!

A Former Brilliant Member - 6 years, 1 month ago

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What do you think was the most incorrect answer that the 40% got wrong?

Lew Sterling Jr - 6 years, 1 month ago

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Maybe ................... 9

A Former Brilliant Member - 6 years, 1 month ago

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@A Former Brilliant Member I guess so.

Lew Sterling Jr - 6 years, 1 month ago
Abhishek Sharma
Apr 21, 2015

9 × x = 81 \sqrt{9 \times x} = 81 Taking 9 9 out, 3 x = 81 3\sqrt{x} = 81 x = 27 \sqrt{x} = 27 Squaring both the sides we get, x = 729 \boxed{x=729}

Atika Samiha
Apr 21, 2015

(9x)=81^2. or.x=(81/3)^2. or,x=27^2=729

Keerthi Lekhya
Apr 21, 2015

9 * x=81 * 81

x=6561/9

x=81

Moderator note:

This would mean that you need to calculate 8 1 2 81^2 then divide by 9 9 . Which is more work than needed.

Mafia maNiAc
Sep 7, 2016

\sqrt{9×x}=81 \Rightarrow 3×\sqrt{x}=81 \Rightarrow \sqrt{x}=27 \Rightarrow x=729 (squaring on both sides)

Ashutosh Tripathi
Dec 16, 2015

sqrt(9*x)=81

3*sqrt(x)=81

sqrt(x)=27

x=729

Since (9x)^1/2=81, then 9x=81^2=9^4. So x=(9^4)/9=9^3=729.

Sunil Kumar
Sep 25, 2015

√9×x=81 Squaring both side 9×x=81×81 X=729

Brian Falcasantos
Sep 25, 2015

More common sense than math. I knew 3 x 27 = 81. So I just squared 27 to get 729.

Moderator note:

Nice shortcut :)

Tootie Frootie
May 10, 2015

whatever operation we do , we do on both the sides , so , we square on both the sides....

Javed Iqbal
Apr 23, 2015

(9 x)^.5=81 squaring both side 9 x=81* 81 x=81* 81/9 x=81* 9 x=729

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