Find the complex conjugate of (2 + 5i)(-4 + 6i).

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(2 + 5i)(-4 + 6i)

Yanam BieapBIEAP Intermediate Board 2018Subjective· 2mImportance★★★★★

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Multiply the two complex numbers first, then flip the sign of the imaginary part to get the conjugate.

First expand the product:

$(2+5i)(-4+6i) = 2(-4) + 2(6i) + 5i(-4) + 5i(6i)$

$= -8 + 12i - 20i + 30i^2$

Since $i^2 = -1$ , $30i^2 = -30$ , so:

$= -8 - 30 + (12i - 20i) = -38 - 8i$ …

Q.Find the complex conjugate of $(2 + 5i)(-4 + 6i)$ .