Expert: Ahmed Salami - 8/8/2004

Question
When x = 1 the function y = 5x² - 10x – 3
a) has a maximum          b) has a minimum
c) is undefined                 d) none of these    ?

(can u show me how you worked it out please)

Answer
Hi liz,
Turning points occur when dy/dx = 0
So for the function
y = 5x² - 10x – 3
dy/dx = 10x - 10
equating this to zero gives
x = 1
A maximun occurs when d²y/dx² is negative and a minimium occurs when it is positive. But
d²y/dx² = 10  which is positive, we therefore have a minimum.
The function is clearly defined for at x = 1, y = -8

I hope it helps.
Regards.