Find x-x 2-9-72A- 7B- 9C- 8D- 10

The correct option is B 9 x^2 9 = 72 ⇒ x^2= 81 ⇒ x = √(81) ⇒ x = √(9 ×9) ∴x = 9 Remember that ( 9)^2 = 81 too. But among the options, the correct answer is 9 ...

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Standard VIII

Mathematics

Finding square root of a number

Find x.x 2-9=...

Question

Find x.

$x^{2} - 9 = 72$

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Solution

The correct option is B
9

$x^{2} - 9 = 72$

$\Rightarrow x^{2} = 81$

$\Rightarrow x = \sqrt[2]{81}$

$\Rightarrow x = \sqrt[2]{9 \times 9}$

$∴$ $x = 9$

Remember that $(- 9)^{2} = 81$ too.
But among the options, the correct answer is 9.

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Find x. x2−9=72

The correct option is B 9 x2−9=72 ⇒x2=81 ⇒x=2√81 ⇒x=2√9×9 ∴x=9 Remember that (−9)2=81 too. But among the options, the correct answer is 9.

Find x.

$x^{2} - 9 = 72$

The correct option is B
9

$x^{2} - 9 = 72$

$\Rightarrow x^{2} = 81$

$\Rightarrow x = \sqrt[2]{81}$

$\Rightarrow x = \sqrt[2]{9 \times 9}$

$∴$ $x = 9$

Remember that $(- 9)^{2} = 81$ too.
But among the options, the correct answer is 9.