heres the question: sketch the curve of y=4-7x-2xsqrd

i get y=4, but to get the two x roots i factorise as normal, and get the solutions x=1/2 and x=+4

however the textbook says that the second root is actually -4...

why?

Printable View

- October 24th 2010, 11:36 AMchartsysketching curves, roots problem
heres the question: sketch the curve of y=4-7x-2xsqrd

i get y=4, but to get the two x roots i factorise as normal, and get the solutions x=1/2 and x=+4

however the textbook says that the second root is actually -4...

why? - October 24th 2010, 11:45 AMmr fantastic
- October 24th 2010, 12:44 PMchartsy
for easiness i will make this smiley face the sign for squared:(Nod)

sketch curve of y=4-7x-2x(Nod)

1) a<0 (-2) so curve is inverted u shape

2) find where it crosses y axis:

subst x=o into eqn

y=4

3)factorise to find the two roots of the curve

0=-2x(Nod)-7x+4

0=-2x(Nod)-8x+x+4

-2x(x-4) 1(x-4)

(-2x+1) (x-4)=0

1)x-4=0

x=4

2)-2x+1=0

x=1/2

so x=1/2 and x=4

so why is it -4? - October 24th 2010, 05:20 PMskeeter
- October 24th 2010, 11:08 PMchartsy
hmmm thanks for that....need to be more focused when factorising then

- October 25th 2010, 03:36 AMmr fantastic