Given that the graph of y=f(x) is symmetric about the y-axis and the gradient of the curve at any point (x, y) is 2x+b. Find the value of b.
If the graph is symmetric about y-axis
then it has a turning point at x=O.
Gradient at turning point =O
"2x+b= 0\\quad at \\>x=0"
"\\implies b=0"
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