SOLUTION: Can you help with this problem? It's a take home exercise that has me stumped: Solve: 2x2 (2x squared) = 7x + 11 I incorrectly listed this under "Word Problems." Thank you.

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equation Customizable Word Problems -> SOLUTION: Can you help with this problem? It's a take home exercise that has me stumped: Solve: 2x2 (2x squared) = 7x + 11 I incorrectly listed this under "Word Problems." Thank you.       Log On


   



Question 110771: Can you help with this problem? It's a take home exercise that has me stumped:
Solve: 2x2 (2x squared) = 7x + 11
I incorrectly listed this under "Word Problems." Thank you.

Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
2x%5E2=7x%2B11 Start with the given equation

0=-2x%5E2%2B7x%2B11 Subtract 2x%5E2 from both sides


Let's use the quadratic formula to solve for x:


Starting with the general quadratic

ax%5E2%2Bbx%2Bc=0

the general solution using the quadratic equation is:

x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29



So lets solve -2%2Ax%5E2%2B7%2Ax%2B11=0 ( notice a=-2, b=7, and c=11)




x+=+%28-7+%2B-+sqrt%28+%287%29%5E2-4%2A-2%2A11+%29%29%2F%282%2A-2%29 Plug in a=-2, b=7, and c=11



x+=+%28-7+%2B-+sqrt%28+49-4%2A-2%2A11+%29%29%2F%282%2A-2%29 Square 7 to get 49



x+=+%28-7+%2B-+sqrt%28+49%2B88+%29%29%2F%282%2A-2%29 Multiply -4%2A11%2A-2 to get 88



x+=+%28-7+%2B-+sqrt%28+137+%29%29%2F%282%2A-2%29 Combine like terms in the radicand (everything under the square root)



x+=+%28-7+%2B-+sqrt%28137%29%29%2F-4 Multiply 2 and -2 to get -4

So now the expression breaks down into two parts

x+=+%28-7+%2B+sqrt%28137%29%29%2F-4 or x+=+%28-7+-+sqrt%28137%29%29%2F-4


Now break up the fraction


x=-7%2F-4%2Bsqrt%28137%29%2F-4 or x=-7%2F-4-sqrt%28137%29%2F-4


Simplify


x=7+%2F+4-sqrt%28137%29%2F4 or x=7+%2F+4%2Bsqrt%28137%29%2F4


So these expressions approximate to

x=-1.17617497767991 or x=4.67617497767991


So our solutions are:
x=-1.17617497767991 or x=4.67617497767991

Notice when we graph -2%2Ax%5E2%2B7%2Ax%2B11, we get:



when we use the root finder feature on a calculator, we find that x=-1.17617497767991 and x=4.67617497767991.So this verifies our answer