Q.

If ω is an imaginary cube root of unity then the equation whose roots are 2ω+3ω2 and 2ω2+3ω is

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a

x2+5x7=0

b

x25x+7=0

c

x25x7=0

d

x2+5x+7=0

answer is A.

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Detailed Solution

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Given that 2ω+3ω2 and 2ω2+3ω are the roots of the equation

here ω is complex cube root of unity, so that 1+ω+ω2=0 and ω3=1

The equation whose roots are 2ω+3ω2 and 2ω2+3ω is     

                x2-x2ω+3ω2+2ω2+3ω+2ω+3ω2·2ω2+3ω=0x2-x5ω+ω2+4+6ω2+6ω+9=0x2-5x-1+13+6-1=0x2+5x+7=0

Therefore, the equation whose roots are 2ω+3ω2 and 2ω2+3ω is x2+5x+7=0

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