WMA11 January 2020

9. WMA11/01 Edexcel IAL P1​​ January​​ 2020, Q9 (Differentiation)

In this question you must show all stages of your working.

Solutions relying on calculator technology are not acceptable.

A​​ curve has equation​​ 

y=4x2+92x        x>0

Find the x coordinate of the point on the curve at which​​ dydx=0

(6)

SOLUTION​​ 

y=4x2+92x12

Spliting the denominator to simplify the equation. ​​ 

y=4x22x12+92x12

y=2x32+92x-12

y=2×32x32-1+92×-12x-12-1

dydx=  3x12-94x-32

When​​ dydx=0

3x12-94x-32=0

x12 -3x-324=0

x12 -34x32=0

4x12+32-3=0

4x2-3=0

4x2=3

x2=34

x=±34

x= ±32

As x>0, rejecting negative value of x.​​ 

x=32