Can you?

Algebra Level 2

(3i+4i)(4i-8i) = ?


The answer is 28.

Brijo Skylite by Brijo Skylite , 21, India

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3 solutions

Aravind Vishnu
Aug 8, 2015

i is common in both the parenthesis and you are done. i 2 = − 1 i \quad\text{is common in both the parenthesis and you are done.}\\ i^2=-1

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Arulx Z
Aug 9, 2015

= ( 3 i + 4 i ) ( 4 i − 8 i ) = 7 i ⋅ − 4 i = − 28 i 2 = 28 =\left( 3i+4i \right) (4i-8i)\\ =7i\cdot -4i\\ =-28{ i }^{ 2 }\\ =28

1 Helpful 0 Interesting 0 Brilliant 0 Confused

Moderator note:

Simple standard approach.

Brijo Skylite
Aug 8, 2015

Multiply i and 3 Multiply i and 1 The i just gets copied along. The answer is i 3 i evaluates to 3i Multiply i and 4 Multiply i and 1 The i just gets copied along. The answer is i 4 i evaluates to 4i 3 i+4 i evaluates to 7i Multiply i and 4 Multiply i and 1 The i just gets copied along. The answer is i 4 i evaluates to 4i Multiply i and 8 Multiply i and 1 The i just gets copied along. The answer is i 8 i evaluates to 8i 4 i-8 i evaluates to -4i Multiply 7i and -4i Multiply the i and i Multiply i and i Combine the i and i by adding the exponents, and keeping the i, to get The answer is (3 i+4 i) (4 i-8*i) evaluates to The final answer (almost!) is Now, let's simplify the i's to get our final answer: The i2 in can be simplified to -1. So, the becomes 28 . The final answer is 28

0 Helpful 0 Interesting 0 Brilliant 0 Confused

Erm... Can u write that in equation form??? Pls?

Christabel Hammond - 5 years, 10 months ago

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Wait a minute.........

Brijo Skylite - 5 years, 10 months ago

3 i 1 i

3i ( When multiplying i 1 =i) 4 I 1*i

4i ( When multiplying i 1 =i) (3 i+4 i) = 7i 8 I 1*i

8i ( When multiplying i 1 =i) (4 i-8 i) = (-4i) From the condition, (3 i+4 i)(4 i-8 i) = (7i)(-4i) [i i=i2 ] =(-28i2 ) =(-28)(-1) [i=√-1] [i2 =-1] =28 The answer is 28.

Brijo Skylite - 5 years, 10 months ago

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