Which of the following is a complex number?

-7
2 + square root 3
4 + 9i
Pie

4 + 9i

Step-by-step explanation:

-7                           negative number, not complex

2 + square root 3    2 + √3   real

4 + 9i                        complex; has real part plus imaginary part

Pie                         pi (not pie):  π       real

+25 = x

step-by-step explanation:

here x is the hypotenuse of a right triangle whose legs are 7 and 24.   by the pythagorean theorem, 7² + 24² must equal x²:

x² = 49 + 576 = 625.   thus, x = +√625 = +25 = x

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