Question

4x^2-81=0 can anyone solve this for me?

Answer 1

4x² - 81 = 0 

4x² = 81 

(2x)² = 81 

2x = √81 

2x = +9 Or -9 

Taking positive, 

2x = 9 

x = 9/2 

:-)

Answer 2

Solution of equation are $\bf \red{ x = \pm \: \frac{9}{2} }$ or $\bf \red{x = \pm \: 4.5}$.

Given:

• $4 {x}^{2} - 81 = 0$

To find:

• Solution of quadratic equation.

Solution:

Identity to be used:

$\bf ( {a}^{2} - {b}^{2} ) = (a + b)(a - b)$

Step 1:

Rewrite the quadratic equation.

$( {2x)}^{2} - ( {9)}^{2} = 0$

Compare with the Identity.

As,

$a = 2x$

and

$b = 9$

Apply Identity.

$\bf (2x + 9)(2x - 9) = 0$

Step 2:

Find the value of x.

As multiplication of two numbers is equal to zero.

so, either first or second number will be zero.

So,

$2x + 9 = 0$

or

$\bf x = \frac{ - 9}{2}$

or

$2x - 9 = 0$

or

$\bf x = \frac{9}{2}$

Thus,

Solution of equation are $\bf x = \pm \: \frac{9}{2}$ or $\bf x = \pm \: 4.5$.

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