SOLUTION: -x^2+7x=4 I changed it to -x^2+ 7x -4 = 0 and quadratic equation would be -b+/- the square root of b^2 -4ac all over 2a. a=-1 b= 7 c= -4 and I got 7.5 and 0.5 but when

Algebra ->  Quadratic Equations and Parabolas  -> Quadratic Equations Lessons  -> Quadratic Equation Lesson -> SOLUTION: -x^2+7x=4 I changed it to -x^2+ 7x -4 = 0 and quadratic equation would be -b+/- the square root of b^2 -4ac all over 2a. a=-1 b= 7 c= -4 and I got 7.5 and 0.5 but when      Log On


   

Question 472171: -x^2+7x=4
I changed it to -x^2+ 7x -4 = 0
and quadratic equation would be -b+/- the square root of b^2 -4ac all over 2a.
a=-1
b= 7
c= -4
and I got 7.5 and 0.5 but when I plug it back in it does not work!
Help is MUCH appreciated!
Found 2 solutions by jim_thompson5910, mananth:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!

-x%5E2%2B7x-4=0 Start with the given equation.


Notice that the quadratic -x%5E2%2B7x-4 is in the form of Ax%5E2%2BBx%2BC where A=-1, B=7, and C=-4


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


x+=+%28-B+%2B-+sqrt%28+B%5E2-4AC+%29%29%2F%282A%29 Start with the quadratic formula


x+=+%28-%287%29+%2B-+sqrt%28+%287%29%5E2-4%28-1%29%28-4%29+%29%29%2F%282%28-1%29%29 Plug in A=-1, B=7, and C=-4


x+=+%28-7+%2B-+sqrt%28+49-4%28-1%29%28-4%29+%29%29%2F%282%28-1%29%29 Square 7 to get 49.


x+=+%28-7+%2B-+sqrt%28+49-16+%29%29%2F%282%28-1%29%29 Multiply 4%28-1%29%28-4%29 to get 16


x+=+%28-7+%2B-+sqrt%28+33+%29%29%2F%282%28-1%29%29 Subtract 16 from 49 to get 33


x+=+%28-7+%2B-+sqrt%28+33+%29%29%2F%28-2%29 Multiply 2 and -1 to get -2.


x+=+%28-7%2Bsqrt%2833%29%29%2F%28-2%29 or x+=+%28-7-sqrt%2833%29%29%2F%28-2%29 Break up the expression.


So the solutions are x+=+%28-7%2Bsqrt%2833%29%29%2F%28-2%29 or x+=+%28-7-sqrt%2833%29%29%2F%28-2%29


These solutions approximate to x+=+0.62771867673099 or x+=+6.37228132326901

Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
Find the roots of the equation by quadratic formula

a= -1 ,b= 7 ,c= -4

b^2-4ac= 49-(-16)
b^2-4ac= 33
sqrt%28%0933%29= 5.74
x=%28-b%2B-sqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=%28-b%2Bsqrt%28b%5E2-4ac%29%29%2F%282a%29
x1=(-7+5.74)/-2
x1= 0.63
x2=(-7-5.74) / -2
x2= 6.37