How do you find the roots, real and imaginary, of y= x^2 - 8x + 15 using the quadratic formula?

1 Answer
sente
Dec 6, 2015

Apply the quadratic formula to find that the roots are x=3 and x=5.

Explanation:

The quadratic formula states that
ax^2 + bx+c = 0 => x = (-b+-sqrt(b^2-4ac))/(2a)
Note that the solutions to x for the initial equation are the roots of
f(x) = ax^2 + bx + c.

Applying that here, we get
x^2 - 8x + 15 = 0

=> x = (-(-8) +- sqrt( (-8)^2-4(15)(1)))/(2(1))

= (8+-sqrt(4))/2

= 4+-1

Thus the roots are x=3 and x=5.

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