Factorize 50. (Complex Algebra)

Algebra Level 3

x = 50 8 i + 6 \large x = \frac{50}{8i+6}

Simplify x x above into the form a + b i a+bi . What is the value of a + b a+b ?

Try first, if you have no idea, see the solutions.

Notation: i = 1 i=\sqrt{-1} denotes the imaginary unit .


The answer is -1.

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3 solutions

Munem Shahriar
Sep 24, 2017

First, we have to simplify x = 50 8 i + 6 x = \dfrac{50}{8i+6}

x = 50 8 i + 6 x = \dfrac{50}{8i+6}

= 50 2 ( 3 + 4 i ) = \dfrac{50}{2(3+4i)}

= 25 ( 3 + 4 i ) = \dfrac{25}{(3+4i)} ~~ ~~ ~ ~ ~~ ~ ~ ; [ 50 2 = 25 ] ; \left[ \dfrac{50}{2} = 25 \right]

= 25 ( 3 4 i ) ( 3 + 4 i ) ( 3 4 i ) = \dfrac{25(3-4i)}{(3+4i)(3-4i)} ~~ ~ ~~ ~ ~ ~ ; [ Multiply by 3 4 i 3 4 i ] ; \left[\text{Multiply by} \dfrac{3-4i}{3-4i} \right]

= 25 ( 3 4 i ) 25 = \dfrac{25(3-4i)}{25}

= 3 4 i = 3-4i

Now a + b i , a + bi, where a = 3 a = 3 and b = 4 b =4

Hence a + b = 3 + ( 4 ) = 1 a + b = 3+ (-4) = \boxed{-1}

Chew-Seong Cheong
Sep 26, 2017

x = 50 8 i + 6 = 50 ( 6 8 i ) ( 6 + 8 i ) ( 6 8 i ) = 50 ( 6 8 i ) 36 + 64 = 3 4 i \begin{aligned} x & = \frac {50}{8i+6} \\ & = \frac {50(6-8i)}{(6+8i)(6-8i)} \\ & = \frac {50(6-8i)}{36+64} \\ & = 3-4i \end{aligned}

a + b = 3 4 = 1 \implies a+b = 3-4= \boxed{-1}

Ron Lauterbach
Sep 23, 2017

( 8 i + 6 ) × ( 3 4 i ) = 50 (8i+6) \times (3-4i) = 50

( 8 i + 6 ) × ( 3 4 i ) = ( 3 × 8 i ) + ( 4 i × 6 ) + ( 3 × 6 ) + ( 4 i × 8 i ) = 24 i 24 i + 18 + 32 = 50 (8i+6) \times (3-4i) = (3 \times 8i) + (-4i \times 6) + (3 \times 6) + (-4i \times 8i) = 24i - 24i + 18 + 32 = 50

( 8 i + 6 ) × ( 3 4 i ) ( 8 i + 6 ) = 3 4 i \frac{(8i+6) \times (3-4i)}{(8i+6)}= 3-4i

3 4 i a + b i 3-4i \equiv a+bi

a = 3 a = 3 , b = 4 b = -4

3 + ( 4 ) = 1 3 + (-4) = -1

1 \boxed{-1}

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