Question

What are the solutions to the equation x2 − 1 = 399?

A. X=20 and x=-20

B. X=200 and x=-200

C. X=400 and x=-400

D. X=398 squared and x=-398 squared

Answer 1

Good evening ,

Answer :

A.

x = ±20

Step-by-step explanation:

x² − 1 = 399 ⇔ x²= 400 ⇌ x² = 20² ⇌ x² − 20² = 0 ⇌ (x-20)(x+20) = 0

⇌ x = 20 or x = -20.

:)

Answer 2

X=20 and x=-20 are the solutions to the equation $x^{2} -1 = 399$

What is a Quadratic equation?

A quadratic equation exists as an algebraic equation of the second degree in x. The quadratic equation in its standard form exists $ax^{2} + bx + c = 0$, where a and b exist as the coefficients, x is the variable, and c stands as the constant term.

Given,

$x^{2} -1 = 399$

To find,

The solutions to the equation.

Step 1

$x^{2} -1 = 399$

Move terms to the left side

$&x^{2}-1=399$

$&x^{2}-1-399=0$

Subtract the numbers

$&x^{2}-1-399=0$

$&x^{2}-400=0$

Use the quadratic formula

$x=\frac{-b \pm \sqrt{b^{2}-4 a c}}{2 a}$

Once in standard form, identify a, b, and c from the original equation and plug them into the quadratic equation.

$&x^{2}-400=0$

a=1

b=0

c=-400

$&x=\frac{-0 \pm \sqrt{0^{2}-4 \cdot 1(-400)}}{2 \cdot 1}$

$&x=\frac{-0 \pm \sqrt{(0^{}-1600)}}{2 }$

$x=\frac{\pm 40}{2}$

$x=\frac{40}{2}$

$x=\frac{-40}{2}$

Hence,

$x=20$

$x=-20$

Thus, Option A. X=20 and x=-20 are the solutions to the equation $x^{2} -1 = 399$

To learn more about Quadratic equations refer to:

https://brainly.com/question/1214333

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