Question

How do you solve ${x^2} + 17 = 0$?

Answer 1

Hint: This equation is the quadratic equation. The general form of the quadratic equation is$a{x^2} + bx + c = 0$. Where ‘a’ is the coefficient of${x^2}$, ‘b’ is the coefficient of x and ‘c’ is the constant term.
To solve this equation, we will apply the quadratic formula for the quadratic equation.
The formula is as below:
$x = \dfrac{{ - b \pm \sqrt {{b^2} - 4ac} }}{{2a}}$ .
Here, $\sqrt {{b^2} - 4ac} $ is called the discriminant. And it is denoted by $\Delta $.
If $\Delta $ is greater than 0, then we will get two distinct and real roots.
If $\Delta $ is less than 0, then we will not get real roots. In this case, we will get two complex numbers.
If $\Delta $ is equal to 0, then we will get two equal real roots.

Complete step by step solution:
Here, the quadratic equation is
${x^2} + 17 = 0$
Let us compare the above expression with $a{x^2} + bx + c = 0$.
Here, we get the value of ‘a’ is 1, the value of ‘b’ is 0, and the value of ‘c’ is 17.
Now, let us find the discriminant $\Delta $.
$ \Rightarrow \Delta = {b^2} - 4ac$
Let us substitute the values.
$ \Rightarrow \Delta = {\left( 0 \right)^2} - 4\left( 1 \right)\left( {17} \right)$
Simplify it.
$ \Rightarrow \Delta = 0 - 68$
Subtract the right-hand side.
$ \Rightarrow \Delta = - 68$
Here, $\Delta $ is less than 0, then we will not get real roots.
Now,
$x = \dfrac{{ - b \pm \sqrt {{b^2} - 4ac} }}{{2a}}$
Put all the values.
$ \Rightarrow x = \dfrac{{ - \left( 0 \right) \pm \sqrt { - 68} }}{{2\left( 1 \right)}}$
That is equal to
$ \Rightarrow x = \dfrac{{0 \pm 2\sqrt { - 17} }}{2}$
That is equal to,
$ \Rightarrow x = \dfrac{{ \pm 2\sqrt {17} i}}{2}$
Let us cancelled out the common factor 2 from the numerator and the denominator:
$ \Rightarrow x = \pm \sqrt {17} i$

Hence, the two factors are $\sqrt {17} i$ and $ - \sqrt {17} i$.

Note:
One important thing is, we can always check our work by multiplying out factors back together, and check that we have got back the original answer.
Here is a list of methods to solve quadratic equations:
Factorization
Completing the square
Using graph
Quadratic formula