Question

Solve the following equations.
x^2+4=0
x^3+4x^2-21x=0
x^4-16=0

options 3,7,1
-7,0,3
2i,-2i
16,-16
2,-2,2i,-2i

Answer 1

x^2+4=0
so, x^2 = -4

x^3+4x^2-21x=0
x (x^2) + 4 (x^2) -21x = 0
x(-4) + 4 (-4) -21x = 0
this is a linear equation in x :)
can you solve it ?

Answer 2

so I would substitute the x for -4? and then solve?

Answer 3

x^2+4 =0
x^2 = -4
so you substitute x^2 as -4 as i did
and you would solve for x from
x(-4) + 4 (-4) -21x = 0

Answer 4

so -4x-16-21x

Answer 5

sorry I get confused easily..

Answer 6

no problem :)
yes thats correct
so,
-25 x = 16
but i don't see that in any choices :P

Answer 7

so it would have to be 16,-16 wouldn't it?

Answer 8

nopes,
x^2 +4 = 0
gives you
x^2 =- 4
x = \(\pm 2i\)

Answer 9

x^4-16 =0
x^4 - 2^4 = (x^2+2^2)(x^2-2^2) = 0
so that x^2-2^2 = 0
gives you 2 other roots
x^2 = 2^2
x= \(\pm 2 \)

Answer 10

so 2,-2,2i,-2i..... I can't figure out the i equations

Answer 11

yes thats correct
you mean you didn't get how we get +2i and -2i ?

Answer 12

I get it but I usually don't

Answer 13

you can ask any doubts :)

Answer 14

i will! will you still help me figure out the other two please? :) I think I get it?

Answer 15

if i am online , i'll help :)

Answer 16

okay so for x^3+4x^2-21x=0 I would enter in a option to see if it works right?

Answer 17

if you have choices, than you can
but easiest thing to do is to factor out 'x'

Answer 18

x(x^2+4x-21) = 0
so, x=0 or
x^2+4x-21 =0

so consider only those choices which have x=0

Answer 19

they both equal 0

Answer 20

so go for
x^2+4x -21 =0
can you tell me 2 numbers whose sum is +4 and product is -21 ?

Answer 21

-25 does

Answer 22

?

Answer 23

-25+4=-21

Answer 24

isn't that what you asked?