Get the ax power of y'=a*e,

So the slope of the tangent at (0, 1) is k=[y'|x=o]=a, and because the tangent is perpendicular to the straight line x+2y+ 1=0,

The slope of the straight line x+2y+ 1=0 is -0.5,

So a *(0.5)=- 1.

So a=2

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