# FP1 Complex numbers question trouble :SWatch

#1
I just have no idea how to do these questions. I've tried to use the examples we've been given, but makes no sense still. Any help?

Find real numbers a and b with a>0 such that
i) (a+bj)^2 = 21+20j
j is the square root of -1 in case you didn't get that.
0
9 years ago
#2
Expand out (a+bj)^2, and then equate real and imaginary parts on both sides. You'll get simultaneous equations to solve.

(If you've seen polar form, it might be less messy to write 21 + 20j in the form R(cos x + i sin x), then take the appropriate square root. But if not, don't worry about it.)
0
#3
(Original post by generalebriety)
Expand out (a+bj)^2, and then equate real and imaginary parts on both sides. You'll get simultaneous equations to solve.

(If you've seen polar form, it might be less messy to write 21 + 20j in the form R(cos x + i sin x), then take the appropriate square root. But if not, don't worry about it.)
Ohh, thanks so much I
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