Maths completeing the square help

[QatarOwnz]

Need help on this question,
why is the answer 1+-(3/2)sq2
question is 2x^2-7=4x

thank you

 

[Shujaat Khan]

x={-b+-√(b^2-4ac)}/2a
a=2, b=-4, c=-7
x={4+-√(72)}/4
x= 1+-(√(4*2*9))/4
x=1+-(6√2)/4
x=1+-(3√2)/4 <----- your answer

If you complete square you get something like this,

x= 1+- 3/√2
then you rationalise by multiplying with √2/√2