ForA=2x^2 –18x+80 (i) find dA/dx , (ii) find the value of x for which A is a minimum
dA/dx = 4x -18 : multiply the number before the x (coefficient) by the power and minus 1 from the power.4x = 18 so x = 4.5 to find the minimum or maximum point, make the differential equal to 0 and solve for x.In order to check if it is a minimum point differentiate the equation again ( dA^2/d^2x = 4) - 4 > 0 and therefore it is a minimum point.
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