Find the maximum value over real x.
Working and explanation
BUILD THE REASONING
Hint 1
A real square is nonnegative.
Hint 2
Multiplication by −2 makes the squared term nonpositive.
Worked solution
Bound the squared term.
Equality is attained at x=1.
Maximum 8 at x=1.
Checks and common pitfalls: The sign of the leading coefficient determines whether the vertex is a maximum or minimum.
Think first. Reveal a hint when the class is ready.