Question

Can someone please help me?

Answer 1

Answer:

A

$\frac{3+5i\sqrt{3} }{2}$ or $\frac{3-5i\sqrt{3} }{2}$ (i cant do the 'plus or minus' sign on my laptop, but the answer is A )

Step-by-step explanation:

f(x)=x²-3x+21

(let f(x)=0)

x²-3x+21=0

Use the quadratic formula

$\frac{-b + \sqrt{b^{2}-4ac } }{2a}$ or $\frac{-b - \sqrt{b^{2}-4ac } }{2a}$

$\frac{-(-3) + \sqrt{(-3)^{2}-4(1)(21) } }{2(1)}$ or $\frac{-(-3) - \sqrt{(-3)^{2}-4(1)(21) } }{2(1)}$

$\frac{3+\sqrt{-75} }{2}$ or $\frac{3-\sqrt{-75} }{2}$

$\frac{3+5i\sqrt{3} }{2}$ or $\frac{3-5i\sqrt{3} }{2}$