Question
Find a and b if :(a + ib) (1 + i) = 2 + i

Answer

(a + ib)(1 + i) = 2 + i a + ai + bi + bi2 = 2 + i

$a+(a+b) i+b(-1)=2+i \ldots \ldots .\left(\because i^2=-1\right)$

(a – b) + (a + b)i = 2 + i Equating real and imaginary parts, we get a – b = 2 ……(i) a + b = 1 …….(ii) Adding equations (i) and (ii), we get 2a = 3

$\therefore a=\frac{3}{2}$

Substituting $a=\frac{3}{2}$ in (ii), we get

$\frac{3}{2}+b=1$

$\therefore b=1-\frac{3}{2}=\frac{-1}{2}$

$\therefore a=\frac{3}{2}$ and $b=\frac{-1}{2}$

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