Q. If z=1+i5−2i, which of the following options is equivalent to z, where the imaginary number i is such that i2=−1?(A) 0(B) i(C) 27(1−i)(D) 23−7i
Multiply by Conjugate: To remove the imaginary number from the denominator, we multiply the numerator and denominator by the complex conjugate of the denominator. The complex conjugate of (1+i) is (1−i).
Expand Numerator and Denominator: Multiplying the numerator and denominator by the complex conjugate, we get:z=(1+i)(1−i)(5−2i)(1−i)
Simplify Expressions: Now we expand the numerator and denominator:Numerator: (5−2i)(1−i)=5−5i−2i+2i2Denominator: (1+i)(1−i)=1−i2
Divide Numerator by Denominator: Since i2=−1, we can simplify the expressions:Numerator: 5−5i−2i−2(−1)=5−5i−2i+2=7−7iDenominator: 1−(−1)=1+1=2
Compare with Options: Now we divide the numerator by the denominator:z = (7−7i)/2This can be written as:z = 7/2 - (7/2)i
Compare with Options: Now we divide the numerator by the denominator:z=27−7iThis can be written as:z=27−(27)iWe compare the result with the given options:z=27−(27)i is equivalent to 27−7i, which matches option C: 7(1−i)/2.
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