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/sci/ - Science & Math

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2159121 No.2159121 [Reply] [Original]

how does I solve

x^2+x-8 ?

>> No.2159135

>>2159129
or factor

>> No.2159129

not an equation, so you don't

>> No.2159145

HERP DERP

>> No.2159154
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2159154

>>2159145

>> No.2159158

factor x

>> No.2159162

use quadratic formula to find solutions as if an equation.

factor as (x-a)(x-b)

where a and b are the solutions found

>> No.2159165

>>2159162
and don't fuck up with sign errors

>> No.2159173
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2159173

can anyone factor this?

>> No.2159177

Find two numbers that add to 1 and multiply to - 8

>> No.2159182

use quadratic formula, silly goose. it's obviously not factorable.

>> No.2159195

x^2+x-8 = 0

The zero part is important. You can use the perfect square method.

(x^2 + x + 1/2 ) - 1/2 + 8 = 0 /So add +1-1 = 0
(x + 1/2)^2 + 7.5 = 0
(x + 1/2)^2 = - 7.5
x + 1/2 = sqrt(7.5)i
x = -1/2 + sqrt(7.5)^0.5i

So the answer is an imaginary number.
sqrt(-1) = i

>> No.2159197

OP here, I'm supposed to find the area inside of the two functions y=x+1 and y=9-x^2 between x=-1 and x=2

now maybe yall can understand

>> No.2159199
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2159199

>> No.2159239

>>2159195
this is riddled with errors

sign errors
not knowing how to square 1/2 errors

hope troll, else sue your math teacher

>> No.2159245

Can't sq root a negative

>> No.2159250

>>2159195
=_<
Draw it. Look at which one is on top or on the bottom. (it's a line and a parabola)
Find interception points with y1 = y2
Integrate using interception points using a method you know.
Simplest is:
The area beneath the bottom line is counted or NOT counted?

>> No.2159254

well this is an integration problem

and you can do it without worrying about where those two lines intersect in this case

also, why the fuck didn't you present the equation not the expression

>> No.2159258

>>2159250
bounds of integration are -1 and 2
not intersects

read OPs post again derp

>> No.2159262

>>2159254
because this is really what I wanted to know

>>2159250
it is counted

>> No.2159269

>>2159245
you can with imaginary number results, but no need in this problem

>> No.2159277

>>2159262
i can't believe you are doing integration problems yet don't know how to solve a quadratic using the quadratic formula or completing the square

>> No.2159290

>>2159239
Riddled by 2 errors. +8 is -8 and 1/2 is 1/4.
(x^2 + x + 1/4 ) - 1/4 - 8 = 0
(x + 1/2)^2 - 8.25 = 0
(x + 1/2)^2 = 8.25
x + 1/2 = sqrt(8.25)
x = -1/2 + sqrt(8.25)

>> No.2159297

>>2159277
Not op. :D

>> No.2159314

>>2159290
you missed the last line, it was a howler

>> No.2159332
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2159332

Derp.
Draw the graph.
Since the parabola (see picture) is above, use that as the top. ∫ (9-x^2) - (x+1) dx =∫ 8 - x - x^2 dx | (-1,2) as boundaries. You get 8x - x^2/2- x^3/3 | (-1,2) which I think gives you 39/2 as your answer.

>> No.2159352

>>2159332
This
http://www.wolframalpha.com/input/?i=area+between+9+-+x%5E2+and+x+%2B+1+from+-1+to+2