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