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# maths help

1. If f(x)=x^4 -8x^3+4x^2+4^x+39 and f(3+2i)= a+ib, then a:b equals?

2. If x= -2- root(3)i  then value of 2x^4+5x^3+7x^2-x+41 is?

please give explanation in detail, thanks

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Anthony B. | Math, Stats, Calculus, APA TutorMath, Stats, Calculus, APA Tutor
4.9 4.9 (381 lesson ratings) (381)
1
Hello Shivam,

f(x)=x4 -8x3+4x2+4x+39
(I'm assuming this was supposed to say 4x rather than 4^x based on the context of the problem.)

1.  f(3+2i)=(3+2i)4-8(3+2i)3+4(3+2i)2+4(3+2i)+39

I'm going to do each term separately starting with the squared one to keep it simple.
4(3+2i)(3+2i)
=4(9+6i+6i+4i2)
Now remember that i2=-1
=4(9+12i-4)
=4(5+12i)
=20+48i

8(3+2i)3
=8(5+12i)(3+2i)      Since we already determined that (3+2i)2=(5+12i)
=8(15+10i+36i+24i2)
=8(15+46i-24)
=8(-9+46i)
=-72+368i

(3+2i)4
=(5+12i)(5+12i)
=25+60i+60i+144i2
=25+120i-144
=-119+120i

Back to the original:
f(3+2i)=-119+120i-72+368i+20+48i+12+8i+39
=-120+544i

Therefore a=-120 and b=544

2. f(x)=2x4+5x3+7x2-x+41
f(-2-√3i)=2(-2-√3i)4+5(-2-√3i)3+7(-2-√3i)2-(-2-√3i)+41

7(-2-√3i)(-2-√3i)
=7(4-2√3i-2√3i+3i2)
=7(4-4√3i-3)
=7(1-4√3i)
=7-28√3i

5(-2-√3i)3
=5(1-4√3i)(-2-√3i)
=5(-2-√3i+8√3i+12i2)
=5(-2+7√3i-12)
=5(-14+7√3i)
=-70+35√3i

7(-2-√3i)4
=7(1-4√3i)(1-4√3i)
=7(1-4√3i-4√3i-48i2)
=7(1-8√3i+48)
=7(49-8√3i)
=343-56√3i

f(-2-√3i)=343-56√3i-70+35√3i+7-28√3i+2+√3i+41
=323-48√3i

In a long operation like this, there are a lot of opportunities for human errors, so you would be wise to run through it twice.