Solve Using the Quadratic Formula y^2-5y+4=0

$y^{2} - 5 y + 4 = 0$

Step 1

Use the quadratic formula to find the solutions.

$\frac{- b \pm \sqrt{b^{2} - 4 (a c)}}{2 a}$

Step 2

Substitute the values $a = 1$ , $b = - 5$ , and $c = 4$ into the quadratic formula and solve for $y$ .

$\frac{5 \pm \sqrt{{(- 5)}^{2} - 4 \cdot (1 \cdot 4)}}{2 \cdot 1}$

Step 3

Simplify.

Simplify the numerator.

Raise $- 5$ to the power of $2$ .

$y = \frac{5 \pm \sqrt{25 - 4 \cdot 1 \cdot 4}}{2 \cdot 1}$

Multiply $- 4 \cdot 1 \cdot 4$ .

Multiply $- 4$ by $1$ .

$y = \frac{5 \pm \sqrt{25 - 4 \cdot 4}}{2 \cdot 1}$

Multiply $- 4$ by $4$ .

$y = \frac{5 \pm \sqrt{25 - 16}}{2 \cdot 1}$

Subtract $16$ from $25$ .

$y = \frac{5 \pm \sqrt{9}}{2 \cdot 1}$

Rewrite $9$ as $3^{2}$ .

$y = \frac{5 \pm \sqrt{3^{2}}}{2 \cdot 1}$

Pull terms out from under the radical, assuming positive real numbers.

$y = \frac{5 \pm 3}{2 \cdot 1}$

Multiply $2$ by $1$ .

$y = \frac{5 \pm 3}{2}$

Step 4

The final answer is the combination of both solutions.

$y = 4, 1$