What is the answer here? Maths!

GottaLovePhysics! :)

17

[Square root of (x+4)] +2 = x

Whats the answer? :confused:

My friend posed this to me today after some test he did

Reply 1

Aphotic Cosmos

17

Wait . . . nope.

Duhhh . . . could be a while.

Reply 2

Mbob

12

Re-arrange so the square root term is the only thing on the left hand side.

Square both sides.

Re-arrange and solve the quadratic.

One of the two solutions will be extraneous so you need to test them both by substitution back in and remove the one that's incorrect.

Reply 3

Susanne839

Original post by Mbob

Re-arrange so the square root term is the only thing on the left hand side.

Square both sides.

Re-arrange and solve the quadratic.

One of the two solutions will be extraneous so you need to test them both by substitution back in and remove the one that's incorrect.

what they said :biggrin:

Reply 4

floralia

http://www.wolframalpha.com/input/?i=solve+sqrt%28x%2B4%29+%2B+2+%3D+x

Man use wolfram alpha! Why don't more people use this thing? Just click show steps. It solves all of your mathematical woes!!! (That said when it starts talking about 25/4 I would have just factorised to give x(x-5) = 0 but hey)

(edited 13 years ago)

Reply 5

limetang

19

(x+4)=(x-2)^2

Expand and you have a lovely quadratic.

Reply 6

limetang

19

Original post by floralia

http://www.wolframalpha.com/input/?i=solve+sqrt%28x%2B4%29+%2B+2+%3D+x

Man use wolfram alpha! Why don't more people use this thing? Just click show steps. It solves all of your mathematical woes!!! (That said when it starts talking about 25/4 I would have just factorised to give x(x-5) = 0 but hey)

Too bad you can't use wolfram alpha in the exam =P

Reply 7

Nomolos

12

[Square root of (x+4)] +2 = x

\sqrt {x+4} = x - 2

(x+4) = x^2 - 4x + 4

0 = x^2 - 5x + 0

0 = x(x-5)

x = 5

This is bad maths on my behalf as it adds x=0 which is incorrect, however, x=5 is the answer you're looking for!

Reply 8

Egor

[Square root of (x+4)] +2 = x
[Square root of (x+4)]= x -2
x + 4 = x*x - 4x +4
x*x - 4x +4 - x - 4 = 0
x*x - 5x = 0
x*x = 5x
x = 5

Reply 9

nonotrly

Or you could just count from 1 until you find the answer (which is by the time you reach 5). >_>

Reply 10

Mbob

12

Original post by nonotrly

Or you could just count from 1 until you find the answer (which is by the time you reach 5). >_>

Unless the answer is 3/2.

Reply 11

nonotrly

Original post by Mbob

Unless the answer is 3/2.

The answer is 5.

Reply 12

Electrodude

7

Original post by floralia

http://www.wolframalpha.com/input/?i=solve+sqrt%28x%2B4%29+%2B+2+%3D+x

Holy ****!? what is this awesome ****??

Reply 13

floralia

Original post by limetang

Too bad you can't use wolfram alpha in the exam =P

Lol yeah but it does explain how to do stuff in a way which is usually easy to follow.

Reply 14

SuperiorHuman

1. Your friend shouldn't be doing maths.
2. You like Physics - even a Physicist should be able to do that. Solve his problem and don't post a whole thread about it. Serious lack of intelligence.
3. Wolfram Alpha if both of you are still to thick to solve this pinch problem.

Reply 15

ilickbatteries

15

No idea what that even means :redface:

Reply 16

limetang

19

Original post by floralia

Lol yeah but it does explain how to do stuff in a way which is usually easy to follow.

True, although I've found it not too helpful when using it to integrate things.

Reply 17

CoolDude

12

Original post by GottaLovePhysics! :)

[Square root of (x+4)] +2 = x

Whats the answer? :confused:

My friend posed this to me today after some test he did

Original post by Egor

[Square root of (x+4)] +2 = x
[Square root of (x+4)]= x -2
x + 4 = x*x - 4x +4
x*x - 4x +4 - x - 4 = 0
x*x - 5x = 0
x*x = 5x
x = 5

Therefore, x=5 or x=0....it's a quadratic equation that touches the x-axis at two points.......so it HAS TWO ANSWERS!!!!!!!

Reply 18

GottaLovePhysics! :)

OP

17

Original post by Egor

[Square root of (x+4)] +2 = x
[Square root of (x+4)]= x -2
x + 4 = x*x - 4x +4
x*x - 4x +4 - x - 4 = 0
x*x - 5x = 0
x*x = 5x
x = 5

Ugh, I told him so! You cant just make x+4=-sqrts + x^2
Thanks for the confirm :tongue:

Original post by SuperiorHuman

1. Your friend shouldn't be doing maths.
2. You like Physics - even a Physicist should be able to do that. Solve his problem and don't post a whole thread about it. Serious lack of intelligence.
3. Wolfram Alpha if both of you are still to thick to solve this pinch problem.