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avatar+732 

\(x(10-x)=40\)

 

solve for x

 Jul 7, 2020
 #1
avatar+21953 
+2

         x(10 - x)  =  40

         10x - x2  =  40

       -x2 + 10x  =  40

-x2 + 10x - 40  =  0

 x2 - 10x + 40  =  0

Quadratic formula with   a = 1   b = -10   c = 40

x  =  [ -(-10) + sqrt( (-10)2 - 4(1)(40) ] ( 2(1) ]

   =  [ 10 + sqrt( 100 - 160 ) ] / 2

   =  [ 10 + sqrt( -60 ) ] / 2

   =  [ 10 + 2sqrt(-15) ] / 2

   =  5 + sqrt(15)·i

 

Other answer:  5 - sqrt(15)·i

 Jul 7, 2020
 #2
avatar+1128 
+2

so we simplify the left side of the equation to get −x^2+10x=40 or 10x-x^2 we then subtract 40 from both sides to get −x^2+10x−40=0 and then we use the quadratic formula to get x=−10+sqrt(−60)−2 or x=−10-sqrt(−60)−2

 Jul 7, 2020
 #3
avatar+732 
0

yeah that's what i initially thought too, but the answer is actually 5 - sqrt(15)·i or  5 + sqrt(15)·i

lokiisnotdead  Jul 10, 2020

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