can someone explain i got the mark scheme but it just doesn't make sense for me | Revision Server | Page 1

rugged grove Dec 22, 2022, 1:21 PM

#

the depth would be the vertical height of it right?

#

aka the magnitude of the y value of the minimum point

rancid quarry Dec 22, 2022, 1:24 PM

#

Oui

mild shard Dec 22, 2022, 1:27 PM

#

#

how do u get

#

1/10(x2 - 30x)

rugged grove Dec 22, 2022, 1:27 PM

#

they factored out 1/10 from x^2 and 3x to get it in a form to complete the square

#

as completing the square gives you the coords of min/max point

#

or you can notice that the curve is symmetrical about x=15 and sub that into equation to find y value

mild shard Dec 22, 2022, 1:45 PM

#

oh so it equals

#

y= 1/10( x^2-30x

rugged grove Dec 22, 2022, 1:46 PM

#

Yes

mild shard Dec 22, 2022, 1:49 PM

#

Y=1/10(x²-30x)=0
Y=1/10(x(x-30))=0
X=0 or X=30

#

can u do that aswell

#

?

#

im condused

#

in this step

#

why do u do that

rugged grove Dec 22, 2022, 2:30 PM

#

when you complete the square, the part inside the bracket is the negative x coord and the bit outside the bracket is y coord

#

e.g (x-a)^2 +b

#

the min point would be (a,b)

#

when you complete the square on 1/10(x^2-30x)

#

you half the x coefficient and change it to (x-15)^2

#

ill draw it

#

#can someone explain i got the mark scheme but it just doesn't make sense for me