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4 votes
I really need help quick

y = x² -4x

find values of x when y=2

with explanation please

1 Answer

14 votes

Answer:


\sf x=2+√(6),\:x=2-√(6)

Step-by-step explanation:


\sf y = x^2 -4x

given that y = 2


\sf x^2 -4x = 2


\sf x^2 -4x -2 = 0

using quadratic formula:


\sf x = ( -b \pm √(b^2 - 4ac))/(2a) \ \ \ when \ ax^2 + bx + c = 0


\rightarrow \sf x_(1,\:2)=(-\left(-4\right)\pm √(\left(-4\right)^2-4\cdot \:1\cdot \left(-2\right)))/(2\cdot \:1)


\rightarrow \sf x_1=(-\left(-4\right)+2√(6))/(2\cdot \:1),\:x_2=(-\left(-4\right)-2√(6))/(2\cdot \:1)


\rightarrow \sf x=2+√(6),\:x=2-√(6)

in decimals:


\rightarrow \sf x=4.45 , \ -0.45

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