Question

Find the values of x³-3x²-8x+15 when x=3+i

Answer 1

Given :  x=3+i

To Find : values of x³- 3x²-8x+15

Solution:

x³- 3x²-8x+15

= x²(x - 3)  - 8x  + 15

x=3+i

=> x - 3 = i

x=3+i

=> x² = 9 + i² + 6i

=> x² = 9 - 1 + 6i

=> x² = 8 + 6i

= (8 + 6i)(i)  - 8(3 + i)  + 15

= 8i  + 6i²  - 24 - 8i  + 15

= 8i  - 6  - 24 - 8i  + 15

= -30 + 15

= - 15

values of x³- 3x²-8x+15   = - 15   when x = 3 + i

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