3. f(x) = x2 + 4x - 2

f(x)= -(x-2)^2+2

Step-by-step explanation:

the same valuve needs the be added to both sides

f(x)+?= -x^2+4x+?-2

to complete the square -x^2+4x-4= -(x-2)^2 add the -4 to the expression

f(x)+?= -x^2+4x-4-2

since -4 was added to the right side, also add -4 the the left side

f(x)-4= -x^2+4x+?-2

now factor out the negative sign from the expression

f(x)-4= -(x^2-4x+4)-2

using a^2-ab+b^2=(a-b)^2

f(x)-4= -(x-2)^2-2

move the constant the the right side and change its sign

f(x)= -(x-2)^2-2+4

now calculate the sum

f(x)= -(x-2)^2+2