Question

A student says that if 5x2 = 20, then x must be equal to 2. Do you agree or disagree with the student? Justify your answer.

Answer 1

I disagree. If each side of the equation is divided by 5, the result is x2 = 4. By the square root property of equality, x = -2 or x = 2. So x could be -2 instead of 2.

Answer 2

we have

$5x^{2}=20$

solve for x

Divide by $5$ both sides

$5x^{2}/5=20/5$

$x^{2}=4$

square root both sides

$\sqrt{x^{2}} =\sqrt{4}$

$x=(+/-)2$

so

the solutions are

$x1=2\\\\x2=-2$

therefore

the answer is

I disagree because x could be $-2$ instead of $2$.